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path: root/include/linux/kvm_host.h
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2025-05-28Merge branch 'kvm-lockdep-common' into HEADPaolo Bonzini
Introduce new mutex locking functions mutex_trylock_nest_lock() and mutex_lock_killable_nest_lock() and use them to clean up locking of all vCPUs for a VM. For x86, this removes some complex code that was used instead of lockdep's "nest_lock" feature. For ARM and RISC-V, this removes a lockdep warning when the VM is configured to have more than MAX_LOCK_DEPTH vCPUs, and removes a fair amount of duplicate code by sharing the logic across all architectures. Signed-off-by: Paolo BOnzini <pbonzini@redhat.com>
2025-05-27KVM: add kvm_lock_all_vcpus and kvm_trylock_all_vcpusMaxim Levitsky
In a few cases, usually in the initialization code, KVM locks all vCPUs of a VM to ensure that userspace doesn't do funny things while KVM performs an operation that affects the whole VM. Until now, all these operations were implemented using custom code, and all of them share the same problem: Lockdep can't cope with simultaneous locking of a large number of locks of the same class. However if these locks are taken while another lock is already held, which is luckily the case, it is possible to take advantage of little known _nest_lock feature of lockdep which allows in this case to have an unlimited number of locks of same class to be taken. To implement this, create two functions: kvm_lock_all_vcpus() and kvm_trylock_all_vcpus() Both functions are needed because some code that will be replaced in the subsequent patches, uses mutex_trylock, instead of regular mutex_lock. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com> Acked-by: Marc Zyngier <maz@kernel.org> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Message-ID: <20250512180407.659015-4-mlevitsk@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-04-24KVM: SVM: Fix SNP AP destroy race with VMRUNTom Lendacky
An AP destroy request for a target vCPU is typically followed by an RMPADJUST to remove the VMSA attribute from the page currently being used as the VMSA for the target vCPU. This can result in a vCPU that is about to VMRUN to exit with #VMEXIT_INVALID. This usually does not happen as APs are typically sitting in HLT when being destroyed and therefore the vCPU thread is not running at the time. However, if HLT is allowed inside the VM, then the vCPU could be about to VMRUN when the VMSA attribute is removed from the VMSA page, resulting in a #VMEXIT_INVALID when the vCPU actually issues the VMRUN and causing the guest to crash. An RMPADJUST against an in-use (already running) VMSA results in a #NPF for the vCPU issuing the RMPADJUST, so the VMSA attribute cannot be changed until the VMRUN for target vCPU exits. The Qemu command line option '-overcommit cpu-pm=on' is an example of allowing HLT inside the guest. Update the KVM_REQ_UPDATE_PROTECTED_GUEST_STATE event to include the KVM_REQUEST_WAIT flag. The kvm_vcpu_kick() function will not wait for requests to be honored, so create kvm_make_request_and_kick() that will add a new event request and honor the KVM_REQUEST_WAIT flag. This will ensure that the target vCPU sees the AP destroy request before returning to the initiating vCPU should the target vCPU be in guest mode. Fixes: e366f92ea99e ("KVM: SEV: Support SEV-SNP AP Creation NAE event") Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com> Link: https://lore.kernel.org/r/fe2c885bf35643dd224e91294edb6777d5df23a4.1743097196.git.thomas.lendacky@amd.com [sean: add a comment explaining the use of smp_send_reschedule()] Co-developed-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-04-07Merge branch 'kvm-tdx-initial' into HEADPaolo Bonzini
This large commit contains the initial support for TDX in KVM. All x86 parts enable the host-side hypercalls that KVM uses to talk to the TDX module, a software component that runs in a special CPU mode called SEAM (Secure Arbitration Mode). The series is in turn split into multiple sub-series, each with a separate merge commit: - Initialization: basic setup for using the TDX module from KVM, plus ioctls to create TDX VMs and vCPUs. - MMU: in TDX, private and shared halves of the address space are mapped by different EPT roots, and the private half is managed by the TDX module. Using the support that was added to the generic MMU code in 6.14, add support for TDX's secure page tables to the Intel side of KVM. Generic KVM code takes care of maintaining a mirror of the secure page tables so that they can be queried efficiently, and ensuring that changes are applied to both the mirror and the secure EPT. - vCPU enter/exit: implement the callbacks that handle the entry of a TDX vCPU (via the SEAMCALL TDH.VP.ENTER) and the corresponding save/restore of host state. - Userspace exits: introduce support for guest TDVMCALLs that KVM forwards to userspace. These correspond to the usual KVM_EXIT_* "heavyweight vmexits" but are triggered through a different mechanism, similar to VMGEXIT for SEV-ES and SEV-SNP. - Interrupt handling: support for virtual interrupt injection as well as handling VM-Exits that are caused by vectored events. Exclusive to TDX are machine-check SMIs, which the kernel already knows how to handle through the kernel machine check handler (commit 7911f145de5f, "x86/mce: Implement recovery for errors in TDX/SEAM non-root mode") - Loose ends: handling of the remaining exits from the TDX module, including EPT violation/misconfig and several TDVMCALL leaves that are handled in the kernel (CPUID, HLT, RDMSR/WRMSR, GetTdVmCallInfo); plus returning an error or ignoring operations that are not supported by TDX guests Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-04-04KVM: Allow building irqbypass.ko as as module when kvm.ko is a moduleSean Christopherson
Convert HAVE_KVM_IRQ_BYPASS into a tristate so that selecting IRQ_BYPASS_MANAGER follows KVM={m,y}, i.e. doesn't force irqbypass.ko to be built-in. Note, PPC allows building KVM as a module, but selects HAVE_KVM_IRQ_BYPASS from a boolean Kconfig, i.e. KVM PPC unnecessarily forces irqbpass.ko to be built-in. But that flaw is a longstanding PPC specific issue. Fixes: 61df71ee992d ("kvm: move "select IRQ_BYPASS_MANAGER" to common code") Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson <seanjc@google.com> Message-ID: <20250315024623.2363994-1-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-03-20Merge branch 'kvm-nvmx-and-vm-teardown' into HEADPaolo Bonzini
The immediate issue being fixed here is a nVMX bug where KVM fails to detect that, after nested VM-Exit, L1 has a pending IRQ (or NMI). However, checking for a pending interrupt accesses the legacy PIC, and x86's kvm_arch_destroy_vm() currently frees the PIC before destroying vCPUs, i.e. checking for IRQs during the forced nested VM-Exit results in a NULL pointer deref; that's a prerequisite for the nVMX fix. The remaining patches attempt to bring a bit of sanity to x86's VM teardown code, which has accumulated a lot of cruft over the years. E.g. KVM currently unloads each vCPU's MMUs in a separate operation from destroying vCPUs, all because when guest SMP support was added, KVM had a kludgy MMU teardown flow that broke when a VM had more than one 1 vCPU. And that oddity lived on, for 18 years... Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-03-14KVM: x86: Move pv_unhalted check out of kvm_vcpu_has_events()Binbin Wu
Move pv_unhalted check out of kvm_vcpu_has_events(), check pv_unhalted explicitly when handling PV unhalt and expose kvm_vcpu_has_events(). kvm_vcpu_has_events() returns true if pv_unhalted is set, and pv_unhalted is only cleared on transitions to KVM_MP_STATE_RUNNABLE. If the guest initiates a spurious wakeup, pv_unhalted could be left set in perpetuity. Currently, this is not problematic because kvm_vcpu_has_events() is only called when handling PV unhalt. However, if kvm_vcpu_has_events() is used for other purposes in the future, it could return the unexpected results. Export kvm_vcpu_has_events() for its usage in broader contexts. Suggested-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com> Message-ID: <20250222014225.897298-3-binbin.wu@linux.intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-03-14KVM: VMX: Initialize TDX during KVM module loadKai Huang
Before KVM can use TDX to create and run TDX guests, TDX needs to be initialized from two perspectives: 1) TDX module must be initialized properly to a working state; 2) A per-cpu TDX initialization, a.k.a the TDH.SYS.LP.INIT SEAMCALL must be done on any logical cpu before it can run any other TDX SEAMCALLs. The TDX host core-kernel provides two functions to do the above two respectively: tdx_enable() and tdx_cpu_enable(). There are two options in terms of when to initialize TDX: initialize TDX at KVM module loading time, or when creating the first TDX guest. Choose to initialize TDX during KVM module loading time: Initializing TDX module is both memory and CPU time consuming: 1) the kernel needs to allocate a non-trivial size(~1/256) of system memory as metadata used by TDX module to track each TDX-usable memory page's status; 2) the TDX module needs to initialize this metadata, one entry for each TDX-usable memory page. Also, the kernel uses alloc_contig_pages() to allocate those metadata chunks, because they are large and need to be physically contiguous. alloc_contig_pages() can fail. If initializing TDX when creating the first TDX guest, then there's chance that KVM won't be able to run any TDX guests albeit KVM _declares_ to be able to support TDX. This isn't good for the user. On the other hand, initializing TDX at KVM module loading time can make sure KVM is providing a consistent view of whether KVM can support TDX to the user. Always only try to initialize TDX after VMX has been initialized. TDX is based on VMX, and if VMX fails to initialize then TDX is likely to be broken anyway. Also, in practice, supporting TDX will require part of VMX and common x86 infrastructure in working order, so TDX cannot be enabled alone w/o VMX support. There are two cases that can result in failure to initialize TDX: 1) TDX cannot be supported (e.g., because of TDX is not supported or enabled by hardware, or module is not loaded, or missing some dependency in KVM's configuration); 2) Any unexpected error during TDX bring-up. For the first case only mark TDX is disabled but still allow KVM module to be loaded. For the second case just fail to load the KVM module so that the user can be aware. Because TDX costs additional memory, don't enable TDX by default. Add a new module parameter 'enable_tdx' to allow the user to opt-in. Note, the name tdx_init() has already been taken by the early boot code. Use tdx_bringup() for initializing TDX (and tdx_cleanup() since KVM doesn't actually teardown TDX). They don't match vt_init()/vt_exit(), vmx_init()/vmx_exit() etc but it's not end of the world. Also, once initialized, the TDX module cannot be disabled and enabled again w/o the TDX module runtime update, which isn't supported by the kernel. After TDX is enabled, nothing needs to be done when KVM disables hardware virtualization, e.g., when offlining CPU, or during suspend/resume. TDX host core-kernel code internally tracks TDX status and can handle "multiple enabling" scenario. Similar to KVM_AMD_SEV, add a new KVM_INTEL_TDX Kconfig to guide KVM TDX code. Make it depend on INTEL_TDX_HOST but not replace INTEL_TDX_HOST because in the longer term there's a use case that requires making SEAMCALLs w/o KVM as mentioned by Dan [1]. Link: https://lore.kernel.org/6723fc2070a96_60c3294dc@dwillia2-mobl3.amr.corp.intel.com.notmuch/ [1] Signed-off-by: Kai Huang <kai.huang@intel.com> Message-ID: <162f9dee05c729203b9ad6688db1ca2960b4b502.1731664295.git.kai.huang@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-03-14KVM: Export hardware virtualization enabling/disabling functionsKai Huang
To support TDX, KVM will need to enable TDX during KVM module loading time. Enabling TDX requires enabling hardware virtualization first so that all online CPUs (and the new CPU going online) are in post-VMXON state. KVM by default enables hardware virtualization but that is done in kvm_init(), which must be the last step after all initialization is done thus is too late for enabling TDX. Export functions to enable/disable hardware virtualization so that TDX code can use them to handle hardware virtualization enabling before kvm_init(). Signed-off-by: Kai Huang <kai.huang@intel.com> Message-ID: <dfe17314c0d9978b7bc3b0833dff6f167fbd28f5.1731664295.git.kai.huang@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-02-26KVM: Drop kvm_arch_sync_events() now that all implementations are nopsSean Christopherson
Remove kvm_arch_sync_events() now that x86 no longer uses it (no other arch has ever used it). No functional change intended. Signed-off-by: Sean Christopherson <seanjc@google.com> Acked-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Reviewed-by: Bibo Mao <maobibo@loongson.cn> Message-ID: <20250224235542.2562848-8-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-02-14KVM: Allow lockless walk of SPTEs when handing aging mmu_notifier eventJames Houghton
It is possible to correctly do aging without taking the KVM MMU lock, or while taking it for read; add a Kconfig to let architectures do so. Architectures that select KVM_MMU_LOCKLESS_AGING are responsible for correctness. Suggested-by: Yu Zhao <yuzhao@google.com> Signed-off-by: James Houghton <jthoughton@google.com> Reviewed-by: David Matlack <dmatlack@google.com> Link: https://lore.kernel.org/r/20250204004038.1680123-3-jthoughton@google.com [sean: massage shortlog+changelog, fix Kconfig goof and shorten name] Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-02-04KVM: remove kvm_arch_post_init_vmPaolo Bonzini
The only statement in a kvm_arch_post_init_vm implementation can be moved into the x86 kvm_arch_init_vm. Do so and remove all traces from architecture-independent code. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2025-01-20Merge branch 'kvm-mirror-page-tables' into HEADPaolo Bonzini
As part of enabling TDX virtual machines, support support separation of private/shared EPT into separate roots. Confidential computing solutions almost invariably have concepts of private and shared memory, but they may different a lot in the details. In SEV, for example, the bit is handled more like a permission bit as far as the page tables are concerned: the private/shared bit is not included in the physical address. For TDX, instead, the bit is more like a physical address bit, with the host mapping private memory in one half of the address space and shared in another. Furthermore, the two halves are mapped by different EPT roots and only the shared half is managed by KVM; the private half (also called Secure EPT in Intel documentation) gets managed by the privileged TDX Module via SEAMCALLs. As a result, the operations that actually change the private half of the EPT are limited and relatively slow compared to reading a PTE. For this reason the design for KVM is to keep a mirror of the private EPT in host memory. This allows KVM to quickly walk the EPT and only perform the slower private EPT operations when it needs to actually modify mid-level private PTEs. There are thus three sets of EPT page tables: external, mirror and direct. In the case of TDX (the only user of this framework) the first two cover private memory, whereas the third manages shared memory: external EPT - Hidden within the TDX module, modified via TDX module calls. mirror EPT - Bookkeeping tree used as an optimization by KVM, not used by the processor. direct EPT - Normal EPT that maps unencrypted shared memory. Managed like the EPT of a normal VM. Modifying external EPT ---------------------- Modifications to the mirrored page tables need to also perform the same operations to the private page tables, which will be handled via kvm_x86_ops. Although this prep series does not interact with the TDX module at all to actually configure the private EPT, it does lay the ground work for doing this. In some ways updating the private EPT is as simple as plumbing PTE modifications through to also call into the TDX module; however, the locking is more complicated because inserting a single PTE cannot anymore be done atomically with a single CMPXCHG. For this reason, the existing FROZEN_SPTE mechanism is used whenever a call to the TDX module updates the private EPT. FROZEN_SPTE acts basically as a spinlock on a PTE. Besides protecting operation of KVM, it limits the set of cases in which the TDX module will encounter contention on its own PTE locks. Zapping external EPT -------------------- While the framework tries to be relatively generic, and to be understandable without knowing TDX much in detail, some requirements of TDX sometimes leak; for example the private page tables also cannot be zapped while the range has anything mapped, so the mirrored/private page tables need to be protected from KVM operations that zap any non-leaf PTEs, for example kvm_mmu_reset_context() or kvm_mmu_zap_all_fast(). For normal VMs, guest memory is zapped for several reasons: user memory getting paged out by the guest, memslots getting deleted, passthrough of devices with non-coherent DMA. Confidential computing adds to these the conversion of memory between shared and privates. These operations must not zap any private memory that is in use by the guest. This is possible because the only zapping that is out of the control of KVM/userspace is paging out userspace memory, which cannot apply to guestmemfd operations. Thus a TDX VM will only zap private memory from memslot deletion and from conversion between private and shared memory which is triggered by the guest. To avoid zapping too much memory, enums are introduced so that operations can choose to target only private or shared memory, and thus only direct or mirror EPT. For example: Memslot deletion - Private and shared MMU notifier based zapping - Shared only Conversion to shared - Private only Conversion to private - Shared only Other cases of zapping will not be supported for KVM, for example APICv update or non-coherent DMA status update; for the latter, TDX will simply require that the CPU supports self-snoop and honor guest PAT unconditionally for shared memory.
2025-01-20Merge tag 'kvm-x86-vcpu_array-6.14' of https://github.com/kvm-x86/linux into ↵Paolo Bonzini
HEAD KVM vcpu_array fixes and cleanups for 6.14: - Explicitly verify the target vCPU is online in kvm_get_vcpu() to fix a bug where KVM would return a pointer to a vCPU prior to it being fully online, and give kvm_for_each_vcpu() similar treatment to fix a similar flaw. - Wait for a vCPU to come online prior to executing a vCPU ioctl to fix a bug where userspace could coerce KVM into handling the ioctl on a vCPU that isn't yet onlined. - Gracefully handle xa_insert() failures even though such failuires should be impossible in practice.
2025-01-14KVM: x86: Drop double-underscores from __kvm_set_memory_region()Sean Christopherson
Now that there's no outer wrapper for __kvm_set_memory_region() and it's static, drop its double-underscore prefix. No functional change intended. Cc: Tao Su <tao1.su@linux.intel.com> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com> Link: https://lore.kernel.org/r/20250111002022.1230573-5-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-01-14KVM: Add a dedicated API for setting KVM-internal memslotsSean Christopherson
Add a dedicated API for setting internal memslots, and have it explicitly disallow setting userspace memslots. Setting a userspace memslots without a direct command from userspace would result in all manner of issues. No functional change intended. Cc: Tao Su <tao1.su@linux.intel.com> Cc: Claudio Imbrenda <imbrenda@linux.ibm.com> Cc: Christian Borntraeger <borntraeger@de.ibm.com> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com> Link: https://lore.kernel.org/r/20250111002022.1230573-4-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2025-01-14KVM: Open code kvm_set_memory_region() into its sole caller (ioctl() API)Sean Christopherson
Open code kvm_set_memory_region() into its sole caller in preparation for adding a dedicated API for setting internal memslots. Oppurtunistically use the fancy new guard(mutex) to avoid a local 'r' variable. Cc: Tao Su <tao1.su@linux.intel.com> Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com> Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com> Acked-by: Christoph Schlameuss <schlameuss@linux.ibm.com> Link: https://lore.kernel.org/r/20250111002022.1230573-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2024-12-23KVM: Add member to struct kvm_gfn_range to indicate private/sharedIsaku Yamahata
Add new members to strut kvm_gfn_range to indicate which mapping (private-vs-shared) to operate on: enum kvm_gfn_range_filter attr_filter. Update the core zapping operations to set them appropriately. TDX utilizes two GPA aliases for the same memslots, one for memory that is for private memory and one that is for shared. For private memory, KVM cannot always perform the same operations it does on memory for default VMs, such as zapping pages and having them be faulted back in, as this requires guest coordination. However, some operations such as guest driven conversion of memory between private and shared should zap private memory. Internally to the MMU, private and shared mappings are tracked on separate roots. Mapping and zapping operations will operate on the respective GFN alias for each root (private or shared). So zapping operations will by default zap both aliases. Add fields in struct kvm_gfn_range to allow callers to specify which aliases so they can only target the aliases appropriate for their specific operation. There was feedback that target aliases should be specified such that the default value (0) is to operate on both aliases. Several options were considered. Several variations of having separate bools defined such that the default behavior was to process both aliases. They either allowed nonsensical configurations, or were confusing for the caller. A simple enum was also explored and was close, but was hard to process in the caller. Instead, use an enum with the default value (0) reserved as a disallowed value. Catch ranges that didn't have the target aliases specified by looking for that specific value. Set target alias with enum appropriately for these MMU operations: - For KVM's mmu notifier callbacks, zap shared pages only because private pages won't have a userspace mapping - For setting memory attributes, kvm_arch_pre_set_memory_attributes() chooses the aliases based on the attribute. - For guest_memfd invalidations, zap private only. Link: https://lore.kernel.org/kvm/ZivIF9vjKcuGie3s@google.com/ Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com> Co-developed-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Signed-off-by: Rick Edgecombe <rick.p.edgecombe@intel.com> Message-ID: <20240718211230.1492011-3-rick.p.edgecombe@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-12-23KVM: guest_memfd: Remove RCU-protected attribute from slot->gmem.fileYan Zhao
Remove the RCU-protected attribute from slot->gmem.file. No need to use RCU primitives rcu_assign_pointer()/synchronize_rcu() to update this pointer. - slot->gmem.file is updated in 3 places: kvm_gmem_bind(), kvm_gmem_unbind(), kvm_gmem_release(). All of them are protected by kvm->slots_lock. - slot->gmem.file is read in 2 paths: (1) kvm_gmem_populate kvm_gmem_get_file __kvm_gmem_get_pfn (2) kvm_gmem_get_pfn kvm_gmem_get_file __kvm_gmem_get_pfn Path (1) kvm_gmem_populate() requires holding kvm->slots_lock, so slot->gmem.file is protected by the kvm->slots_lock in this path. Path (2) kvm_gmem_get_pfn() does not require holding kvm->slots_lock. However, it's also not guarded by rcu_read_lock() and rcu_read_unlock(). So synchronize_rcu() in kvm_gmem_unbind()/kvm_gmem_release() actually will not wait for the readers in kvm_gmem_get_pfn() due to lack of RCU read-side critical section. The path (2) kvm_gmem_get_pfn() is safe without RCU protection because: a) kvm_gmem_bind() is called on a new memslot, before the memslot is visible to kvm_gmem_get_pfn(). b) kvm->srcu ensures that kvm_gmem_unbind() and freeing of a memslot occur after the memslot is no longer visible to kvm_gmem_get_pfn(). c) get_file_active() ensures that kvm_gmem_get_pfn() will not access the stale file if kvm_gmem_release() sets it to NULL. This is because if kvm_gmem_release() occurs before kvm_gmem_get_pfn(), get_file_active() will return NULL; if get_file_active() does not return NULL, kvm_gmem_release() should not occur until after kvm_gmem_get_pfn() releases the file reference. Signed-off-by: Yan Zhao <yan.y.zhao@intel.com> Message-ID: <20241104084303.29909-1-yan.y.zhao@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-12-16KVM: Verify there's at least one online vCPU when iterating over all vCPUsSean Christopherson
Explicitly check that there is at least online vCPU before iterating over all vCPUs. Because the max index is an unsigned long, passing "0 - 1" in the online_vcpus==0 case results in xa_for_each_range() using an unlimited max, i.e. allows it to access vCPU0 when it shouldn't. This will allow KVM to safely _erase_ from vcpu_array if the last stages of vCPU creation fail, i.e. without generating a use-after-free if a different task happens to be concurrently iterating over all vCPUs. Note, because xa_for_each_range() is a macro, kvm_for_each_vcpu() subtly reloads online_vcpus after each iteration, i.e. adding an extra load doesn't meaningfully impact the total cost of iterating over all vCPUs. And because online_vcpus is never decremented, there is no risk of a reload triggering a walk of the entire xarray. Cc: Will Deacon <will@kernel.org> Cc: Michal Luczaj <mhal@rbox.co> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20241009150455.1057573-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2024-12-16KVM: Explicitly verify target vCPU is online in kvm_get_vcpu()Sean Christopherson
Explicitly verify the target vCPU is fully online _prior_ to clamping the index in kvm_get_vcpu(). If the index is "bad", the nospec clamping will generate '0', i.e. KVM will return vCPU0 instead of NULL. In practice, the bug is unlikely to cause problems, as it will only come into play if userspace or the guest is buggy or misbehaving, e.g. KVM may send interrupts to vCPU0 instead of dropping them on the floor. However, returning vCPU0 when it shouldn't exist per online_vcpus is problematic now that KVM uses an xarray for the vCPUs array, as KVM needs to insert into the xarray before publishing the vCPU to userspace (see commit c5b077549136 ("KVM: Convert the kvm->vcpus array to a xarray")), i.e. before vCPU creation is guaranteed to succeed. As a result, incorrectly providing access to vCPU0 will trigger a use-after-free if vCPU0 is dereferenced and kvm_vm_ioctl_create_vcpu() bails out of vCPU creation due to an error and frees vCPU0. Commit afb2acb2e3a3 ("KVM: Fix vcpu_array[0] races") papered over that issue, but in doing so introduced an unsolvable teardown conundrum. Preventing accesses to vCPU0 before it's fully online will allow reverting commit afb2acb2e3a3, without re-introducing the vcpu_array[0] UAF race. Fixes: 1d487e9bf8ba ("KVM: fix spectrev1 gadgets") Cc: stable@vger.kernel.org Cc: Will Deacon <will@kernel.org> Cc: Michal Luczaj <mhal@rbox.co> Reviewed-by: Pankaj Gupta <pankaj.gupta@amd.com> Acked-by: Will Deacon <will@kernel.org> Link: https://lore.kernel.org/r/20241009150455.1057573-2-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2024-11-14KVM: x86: switch hugepage recovery thread to vhost_taskPaolo Bonzini
kvm_vm_create_worker_thread() is meant to be used for kthreads that can consume significant amounts of CPU time on behalf of a VM or in response to how the VM behaves (for example how it accesses its memory). Therefore it wants to charge the CPU time consumed by that work to the VM's container. However, because of these threads, cgroups which have kvm instances inside never complete freezing. This can be trivially reproduced: root@test ~# mkdir /sys/fs/cgroup/test root@test ~# echo $$ > /sys/fs/cgroup/test/cgroup.procs root@test ~# qemu-system-x86_64 -nographic -enable-kvm and in another terminal: root@test ~# echo 1 > /sys/fs/cgroup/test/cgroup.freeze root@test ~# cat /sys/fs/cgroup/test/cgroup.events populated 1 frozen 0 The cgroup freezing happens in the signal delivery path but kvm_nx_huge_page_recovery_worker, while joining non-root cgroups, never calls into the signal delivery path and thus never gets frozen. Because the cgroup freezer determines whether a given cgroup is frozen by comparing the number of frozen threads to the total number of threads in the cgroup, the cgroup never becomes frozen and users waiting for the state transition may hang indefinitely. Since the worker kthread is tied to a user process, it's better if it behaves similarly to user tasks as much as possible, including being able to send SIGSTOP and SIGCONT. In fact, vhost_task is all that kvm_vm_create_worker_thread() wanted to be and more: not only it inherits the userspace process's cgroups, it has other niceties like being parented properly in the process tree. Use it instead of the homegrown alternative. Incidentally, the new code is also better behaved when you flip recovery back and forth to disabled and back to enabled. If your recovery period is 1 minute, it will run the next recovery after 1 minute independent of how many times you flipped the parameter. (Commit message based on emails from Tejun). Reported-by: Tejun Heo <tj@kernel.org> Reported-by: Luca Boccassi <bluca@debian.org> Acked-by: Tejun Heo <tj@kernel.org> Tested-by: Luca Boccassi <bluca@debian.org> Cc: stable@vger.kernel.org Reviewed-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-11-14Merge tag 'loongarch-kvm-6.13' of ↵Paolo Bonzini
git://git.kernel.org/pub/scm/linux/kernel/git/chenhuacai/linux-loongson into HEAD LoongArch KVM changes for v6.13 1. Add iocsr and mmio bus simulation in kernel. 2. Add in-kernel interrupt controller emulation. 3. Add virt extension support for eiointc irqchip.
2024-11-13LoongArch: KVM: Add iocsr and mmio bus simulation in kernelXianglai Li
Add iocsr and mmio memory read and write simulation to the kernel. When the VM accesses the device address space through iocsr instructions or mmio, it does not need to return to the qemu user mode but can directly completes the access in the kernel mode. Signed-off-by: Tianrui Zhao <zhaotianrui@loongson.cn> Signed-off-by: Xianglai Li <lixianglai@loongson.cn> Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
2024-10-30KVM: Protect vCPU's "last run PID" with rwlock, not RCUSean Christopherson
To avoid jitter on KVM_RUN due to synchronize_rcu(), use a rwlock instead of RCU to protect vcpu->pid, a.k.a. the pid of the task last used to a vCPU. When userspace is doing M:N scheduling of tasks to vCPUs, e.g. to run SEV migration helper vCPUs during post-copy, the synchronize_rcu() needed to change the PID associated with the vCPU can stall for hundreds of milliseconds, which is problematic for latency sensitive post-copy operations. In the directed yield path, do not acquire the lock if it's contended, i.e. if the associated PID is changing, as that means the vCPU's task is already running. Reported-by: Steve Rutherford <srutherford@google.com> Reviewed-by: Steve Rutherford <srutherford@google.com> Acked-by: Oliver Upton <oliver.upton@linux.dev> Link: https://lore.kernel.org/r/20240802200136.329973-3-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com>
2024-10-25KVM: Don't grab reference on VM_MIXEDMAP pfns that have a "struct page"Sean Christopherson
Now that KVM no longer relies on an ugly heuristic to find its struct page references, i.e. now that KVM can't get false positives on VM_MIXEDMAP pfns, remove KVM's hack to elevate the refcount for pfns that happen to have a valid struct page. In addition to removing a long-standing wart in KVM, this allows KVM to map non-refcounted struct page memory into the guest, e.g. for exposing GPU TTM buffers to KVM guests. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-86-seanjc@google.com>
2024-10-25KVM: Drop APIs that manipulate "struct page" via pfnsSean Christopherson
Remove all kvm_{release,set}_pfn_*() APIs now that all users are gone. No functional change intended. Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-85-seanjc@google.com>
2024-10-25KVM: Drop gfn_to_pfn() APIs now that all users are goneSean Christopherson
Drop gfn_to_pfn() and all its variants now that all users are gone. No functional change intended. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-80-seanjc@google.com>
2024-10-25KVM: Add support for read-only usage of gfn_to_page()Sean Christopherson
Rework gfn_to_page() to support read-only accesses so that it can be used by arm64 to get MTE tags out of guest memory. Opportunistically rewrite the comment to be even more stern about using gfn_to_page(), as there are very few scenarios where requiring a struct page is actually the right thing to do (though there are such scenarios). Add a FIXME to call out that KVM probably should be pinning pages, not just getting pages. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-77-seanjc@google.com>
2024-10-25KVM: Move x86's API to release a faultin page to common KVMSean Christopherson
Move KVM x86's helper that "finishes" the faultin process to common KVM so that the logic can be shared across all architectures. Note, not all architectures implement a fast page fault path, but the gist of the comment applies to all architectures. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-50-seanjc@google.com>
2024-10-25KVM: guest_memfd: Provide "struct page" as output from kvm_gmem_get_pfn()Sean Christopherson
Provide the "struct page" associated with a guest_memfd pfn as an output from __kvm_gmem_get_pfn() so that KVM guest page fault handlers can directly put the page instead of having to rely on kvm_pfn_to_refcounted_page(). Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-47-seanjc@google.com>
2024-10-25KVM: Add kvm_faultin_pfn() to specifically service guest page faultsSean Christopherson
Add a new dedicated API, kvm_faultin_pfn(), for servicing guest page faults, i.e. for getting pages/pfns that will be mapped into the guest via an mmu_notifier-protected KVM MMU. Keep struct kvm_follow_pfn buried in internal code, as having __kvm_faultin_pfn() take "out" params is actually cleaner for several architectures, e.g. it allows the caller to have its own "page fault" structure without having to marshal data to/from kvm_follow_pfn. Long term, common KVM would ideally provide a kvm_page_fault structure, a la x86's struct of the same name. But all architectures need to be converted to a common API before that can happen. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-44-seanjc@google.com>
2024-10-25KVM: Move declarations of memslot accessors up in kvm_host.hSean Christopherson
Move the memslot lookup helpers further up in kvm_host.h so that they can be used by inlined "to pfn" wrappers. No functional change intended. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-43-seanjc@google.com>
2024-10-25KVM: Pass in write/dirty to kvm_vcpu_map(), not kvm_vcpu_unmap()Sean Christopherson
Now that all kvm_vcpu_{,un}map() users pass "true" for @dirty, have them pass "true" as a @writable param to kvm_vcpu_map(), and thus create a read-only mapping when possible. Note, creating read-only mappings can be theoretically slower, as they don't play nice with fast GUP due to the need to break CoW before mapping the underlying PFN. But practically speaking, creating a mapping isn't a super hot path, and getting a writable mapping for reading is weird and confusing. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-34-seanjc@google.com>
2024-10-25KVM: Pin (as in FOLL_PIN) pages during kvm_vcpu_map()Sean Christopherson
Pin, as in FOLL_PIN, pages when mapping them for direct access by KVM. As per Documentation/core-api/pin_user_pages.rst, writing to a page that was gotten via FOLL_GET is explicitly disallowed. Correct (uses FOLL_PIN calls): pin_user_pages() write to the data within the pages unpin_user_pages() INCORRECT (uses FOLL_GET calls): get_user_pages() write to the data within the pages put_page() Unfortunately, FOLL_PIN is a "private" flag, and so kvm_follow_pfn must use a one-off bool instead of being able to piggyback the "flags" field. Link: https://lwn.net/Articles/930667 Link: https://lore.kernel.org/all/cover.1683044162.git.lstoakes@gmail.com Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-32-seanjc@google.com>
2024-10-25KVM: Migrate kvm_vcpu_map() to kvm_follow_pfn()David Stevens
Migrate kvm_vcpu_map() to kvm_follow_pfn(), and have it track whether or not the map holds a refcounted struct page. Precisely tracking struct page references will eventually allow removing kvm_pfn_to_refcounted_page() and its various wrappers. Signed-off-by: David Stevens <stevensd@chromium.org> [sean: use a pointer instead of a boolean] Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-31-seanjc@google.com>
2024-10-25KVM: Use NULL for struct page pointer to indicate mremapped memorySean Christopherson
Drop yet another unnecessary magic page value from KVM, as there's zero reason to use a poisoned pointer to indicate "no page". If KVM uses a NULL page pointer, the kernel will explode just as quickly as if KVM uses a poisoned pointer. Never mind the fact that such usage would be a blatant and egregious KVM bug. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-23-seanjc@google.com>
2024-10-25KVM: Drop unused "hva" pointer from __gfn_to_pfn_memslot()Sean Christopherson
Drop @hva from __gfn_to_pfn_memslot() now that all callers pass NULL. No functional change intended. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-19-seanjc@google.com>
2024-10-25KVM: Replace "async" pointer in gfn=>pfn with "no_wait" and error codeDavid Stevens
Add a pfn error code to communicate that hva_to_pfn() failed because I/O was needed and disallowed, and convert @async to a constant @no_wait boolean. This will allow eliminating the @no_wait param by having callers pass in FOLL_NOWAIT along with other FOLL_* flags. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: David Stevens <stevensd@chromium.org> Co-developed-by: Sean Christopherson <seanjc@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-17-seanjc@google.com>
2024-10-25KVM: Drop @atomic param from gfn=>pfn and hva=>pfn APIsSean Christopherson
Drop @atomic from the myriad "to_pfn" APIs now that all callers pass "false", and remove a comment blurb about KVM running only the "GUP fast" part in atomic context. No functional change intended. Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-13-seanjc@google.com>
2024-10-25KVM: Rename gfn_to_page_many_atomic() to kvm_prefetch_pages()Sean Christopherson
Rename gfn_to_page_many_atomic() to kvm_prefetch_pages() to try and communicate its true purpose, as the "atomic" aspect is essentially a side effect of the fact that x86 uses the API while holding mmu_lock. E.g. even if mmu_lock weren't held, KVM wouldn't want to fault-in pages, as the goal is to opportunistically grab surrounding pages that have already been accessed and/or dirtied by the host, and to do so quickly. Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-12-seanjc@google.com>
2024-10-25KVM: Add kvm_release_page_unused() API to put pages that KVM never consumesSean Christopherson
Add an API to release an unused page, i.e. to put a page without marking it accessed or dirty. The API will be used when KVM faults-in a page but bails before installing the guest mapping (and other similar flows). Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-4-seanjc@google.com>
2024-10-25KVM: Drop KVM_ERR_PTR_BAD_PAGE and instead return NULL to indicate an errorSean Christopherson
Remove KVM_ERR_PTR_BAD_PAGE and instead return NULL, as "bad page" is just a leftover bit of weirdness from days of old when KVM stuffed a "bad" page into the guest instead of actually handling missing pages. See commit cea7bb21280e ("KVM: MMU: Make gfn_to_page() always safe"). Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Tested-by: Alex Bennée <alex.bennee@linaro.org> Signed-off-by: Sean Christopherson <seanjc@google.com> Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-ID: <20241010182427.1434605-2-seanjc@google.com>
2024-10-20KVM: Remove unused kvm_vcpu_gfn_to_pfn_atomicDr. David Alan Gilbert
The last use of kvm_vcpu_gfn_to_pfn_atomic was removed by commit 1bbc60d0c7e5 ("KVM: x86/mmu: Remove MMU auditing") Remove it. Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org> Message-ID: <20241001141354.18009-3-linux@treblig.org> [Adjust Documentation/virt/kvm/locking.rst. - Paolo] Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-10-20KVM: Remove unused kvm_vcpu_gfn_to_pfnDr. David Alan Gilbert
The last use of kvm_vcpu_gfn_to_pfn was removed by commit b1624f99aa8f ("KVM: Remove kvm_vcpu_gfn_to_page() and kvm_vcpu_gpa_to_page()") Remove it. Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org> Message-ID: <20241001141354.18009-2-linux@treblig.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-09-17Merge branch 'kvm-redo-enable-virt' into HEADPaolo Bonzini
Register KVM's cpuhp and syscore callbacks when enabling virtualization in hardware, as the sole purpose of said callbacks is to disable and re-enable virtualization as needed. The primary motivation for this series is to simplify dealing with enabling virtualization for Intel's TDX, which needs to enable virtualization when kvm-intel.ko is loaded, i.e. long before the first VM is created. That said, this is a nice cleanup on its own. By registering the callbacks on-demand, the callbacks themselves don't need to check kvm_usage_count, because their very existence implies a non-zero count. Patch 1 (re)adds a dedicated lock for kvm_usage_count. This avoids a lock ordering issue between cpus_read_lock() and kvm_lock. The lock ordering issue still exist in very rare cases, and will be fixed for good by switching vm_list to an (S)RCU-protected list. Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-09-04KVM: Add arch hooks for enabling/disabling virtualizationSean Christopherson
Add arch hooks that are invoked when KVM enables/disable virtualization. x86 will use the hooks to register an "emergency disable" callback, which is essentially an x86-specific shutdown notifier that is used when the kernel is doing an emergency reboot/shutdown/kexec. Add comments for the declarations to help arch code understand exactly when the callbacks are invoked. Alternatively, the APIs themselves could communicate most of the same info, but kvm_arch_pre_enable_virtualization() and kvm_arch_post_disable_virtualization() are a bit cumbersome, and make it a bit less obvious that they are intended to be implemented as a pair. Reviewed-by: Chao Gao <chao.gao@intel.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Acked-by: Kai Huang <kai.huang@intel.com> Tested-by: Farrah Chen <farrah.chen@intel.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-ID: <20240830043600.127750-9-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-09-04KVM: Rename arch hooks related to per-CPU virtualization enablingSean Christopherson
Rename the per-CPU hooks used to enable virtualization in hardware to align with the KVM-wide helpers in kvm_main.c, and to better capture that the callbacks are invoked on every online CPU. No functional change intended. Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Reviewed-by: Kai Huang <kai.huang@intel.com> Message-ID: <20240830043600.127750-5-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-09-04kvm: Note an RCU quiescent state on guest exitLeonardo Bras
As of today, KVM notes a quiescent state only in guest entry, which is good as it avoids the guest being interrupted for current RCU operations. While the guest vcpu runs, it can be interrupted by a timer IRQ that will check for any RCU operations waiting for this CPU. In case there are any of such, it invokes rcu_core() in order to sched-out the current thread and note a quiescent state. This occasional schedule work will introduce tens of microsseconds of latency, which is really bad for vcpus running latency-sensitive applications, such as real-time workloads. So, note a quiescent state in guest exit, so the interrupted guests is able to deal with any pending RCU operations before being required to invoke rcu_core(), and thus avoid the overhead of related scheduler work. Signed-off-by: Leonardo Bras <leobras@redhat.com> Acked-by: Paul E. McKenney <paulmck@kernel.org> Acked-by: Sean Christopherson <seanjc@google.com> Message-ID: <20240511020557.1198200-1-leobras@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2024-08-14KVM: x86: Disallow read-only memslots for SEV-ES and SEV-SNP (and TDX)Sean Christopherson
Disallow read-only memslots for SEV-{ES,SNP} VM types, as KVM can't directly emulate instructions for ES/SNP, and instead the guest must explicitly request emulation. Unless the guest explicitly requests emulation without accessing memory, ES/SNP relies on KVM creating an MMIO SPTE, with the subsequent #NPF being reflected into the guest as a #VC. But for read-only memslots, KVM deliberately doesn't create MMIO SPTEs, because except for ES/SNP, doing so requires setting reserved bits in the SPTE, i.e. the SPTE can't be readable while also generating a #VC on writes. Because KVM never creates MMIO SPTEs and jumps directly to emulation, the guest never gets a #VC. And since KVM simply resumes the guest if ES/SNP guests trigger emulation, KVM effectively puts the vCPU into an infinite #NPF loop if the vCPU attempts to write read-only memory. Disallow read-only memory for all VMs with protected state, i.e. for upcoming TDX VMs as well as ES/SNP VMs. For TDX, it's actually possible to support read-only memory, as TDX uses EPT Violation #VE to reflect the fault into the guest, e.g. KVM could configure read-only SPTEs with RX protections and SUPPRESS_VE=0. But there is no strong use case for supporting read-only memslots on TDX, e.g. the main historical usage is to emulate option ROMs, but TDX disallows executing from shared memory. And if someone comes along with a legitimate, strong use case, the restriction can always be lifted for TDX. Don't bother trying to retroactively apply the restriction to SEV-ES VMs that are created as type KVM_X86_DEFAULT_VM. Read-only memslots can't possibly work for SEV-ES, i.e. disallowing such memslots is really just means reporting an error to userspace instead of silently hanging vCPUs. Trying to deal with the ordering between KVM_SEV_INIT and memslot creation isn't worth the marginal benefit it would provide userspace. Fixes: 26c44aa9e076 ("KVM: SEV: define VM types for SEV and SEV-ES") Fixes: 1dfe571c12cf ("KVM: SEV: Add initial SEV-SNP support") Cc: Peter Gonda <pgonda@google.com> Cc: Michael Roth <michael.roth@amd.com> Cc: Vishal Annapurve <vannapurve@google.com> Cc: Ackerly Tng <ackerleytng@google.com> Signed-off-by: Sean Christopherson <seanjc@google.com> Message-ID: <20240809190319.1710470-2-seanjc@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>