diff options
Diffstat (limited to 'Documentation/virt/kvm/api.rst')
| -rw-r--r-- | Documentation/virt/kvm/api.rst | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 544fb11351d9..6aa40ee05a4a 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -2006,7 +2006,7 @@ frequency is KHz. If the KVM_CAP_VM_TSC_CONTROL capability is advertised, this can also be used as a vm ioctl to set the initial tsc frequency of subsequently -created vCPUs. +created vCPUs. Note, the vm ioctl is only allowed prior to creating vCPUs. For TSC protected Confidential Computing (CoCo) VMs where TSC frequency is configured once at VM scope and remains unchanged during VM's @@ -7851,6 +7851,7 @@ Valid bits in args[0] are:: #define KVM_X86_DISABLE_EXITS_HLT (1 << 1) #define KVM_X86_DISABLE_EXITS_PAUSE (1 << 2) #define KVM_X86_DISABLE_EXITS_CSTATE (1 << 3) + #define KVM_X86_DISABLE_EXITS_APERFMPERF (1 << 4) Enabling this capability on a VM provides userspace with a way to no longer intercept some instructions for improved latency in some @@ -7861,6 +7862,28 @@ all such vmexits. Do not enable KVM_FEATURE_PV_UNHALT if you disable HLT exits. +Virtualizing the ``IA32_APERF`` and ``IA32_MPERF`` MSRs requires more +than just disabling APERF/MPERF exits. While both Intel and AMD +document strict usage conditions for these MSRs--emphasizing that only +the ratio of their deltas over a time interval (T0 to T1) is +architecturally defined--simply passing through the MSRs can still +produce an incorrect ratio. + +This erroneous ratio can occur if, between T0 and T1: + +1. The vCPU thread migrates between logical processors. +2. Live migration or suspend/resume operations take place. +3. Another task shares the vCPU's logical processor. +4. C-states lower than C0 are emulated (e.g., via HLT interception). +5. The guest TSC frequency doesn't match the host TSC frequency. + +Due to these complexities, KVM does not automatically associate this +passthrough capability with the guest CPUID bit, +``CPUID.6:ECX.APERFMPERF[bit 0]``. Userspace VMMs that deem this +mechanism adequate for virtualizing the ``IA32_APERF`` and +``IA32_MPERF`` MSRs must set the guest CPUID bit explicitly. + + 7.14 KVM_CAP_S390_HPAGE_1M -------------------------- @@ -8387,7 +8410,7 @@ core crystal clock frequency, if a non-zero CPUID 0x15 is exposed to the guest. 7.36 KVM_CAP_DIRTY_LOG_RING/KVM_CAP_DIRTY_LOG_RING_ACQ_REL ---------------------------------------------------------- -:Architectures: x86, arm64 +:Architectures: x86, arm64, riscv :Type: vm :Parameters: args[0] - size of the dirty log ring @@ -8599,7 +8622,7 @@ ENOSYS for the others. When enabled, KVM will exit to userspace with KVM_EXIT_SYSTEM_EVENT of type KVM_SYSTEM_EVENT_SUSPEND to process the guest suspend request. -7.37 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS +7.42 KVM_CAP_ARM_WRITABLE_IMP_ID_REGS ------------------------------------- :Architectures: arm64 @@ -8628,6 +8651,17 @@ given VM. When this capability is enabled, KVM resets the VCPU when setting MP_STATE_INIT_RECEIVED through IOCTL. The original MP_STATE is preserved. +7.43 KVM_CAP_ARM_CACHEABLE_PFNMAP_SUPPORTED +------------------------------------------- + +:Architectures: arm64 +:Target: VM +:Parameters: None + +This capability indicate to the userspace whether a PFNMAP memory region +can be safely mapped as cacheable. This relies on the presence of +force write back (FWB) feature support on the hardware. + 8. Other capabilities. ====================== |