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2023-11-27powerpc/lib: Validate size for vector operationsNaveen N Rao
Some of the fp/vmx code in sstep.c assume a certain maximum size for the instructions being emulated. The size of those operations however is determined separately in analyse_instr(). Add a check to validate the assumption on the maximum size of the operations, so as to prevent any unintended kernel stack corruption. Signed-off-by: Naveen N Rao <naveen@kernel.org> Reviewed-by: Gustavo A. R. Silva <gustavoars@kernel.org> Build-tested-by: Gustavo A. R. Silva <gustavoars@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231123071705.397625-1-naveen@kernel.org
2023-11-27powerpc/lib: Avoid array bounds warnings in vec opsMichael Ellerman
Building with GCC with -Warray-bounds enabled there are several warnings in sstep.c along the lines of: In function ‘do_byte_reverse’, inlined from ‘do_vec_load’ at arch/powerpc/lib/sstep.c:691:3, inlined from ‘emulate_loadstore’ at arch/powerpc/lib/sstep.c:3439:9: arch/powerpc/lib/sstep.c:289:23: error: array subscript 2 is outside array bounds of ‘u8[16]’ {aka ‘unsigned char[16]’} [-Werror=array-bounds=] 289 | up[2] = byterev_8(up[1]); | ~~~~~~^~~~~~~~~~~~~~~~~~ arch/powerpc/lib/sstep.c: In function ‘emulate_loadstore’: arch/powerpc/lib/sstep.c:681:11: note: at offset 16 into object ‘u’ of size 16 681 | } u = {}; | ^ do_byte_reverse() supports a size up to 32 bytes, but in these cases the caller is only passing a 16 byte buffer. In practice there is no bug, do_vec_load() is only called from the LOAD_VMX case in emulate_loadstore(). That in turn is only reached when analyse_instr() recognises VMX ops, and in all cases the size is no greater than 16: $ git grep -w LOAD_VMX arch/powerpc/lib/sstep.c arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 1); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 2); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 4); arch/powerpc/lib/sstep.c: op->type = MKOP(LOAD_VMX, 0, 16); Similarly for do_vec_store(). Although the warning is incorrect, the code would be safer if it clamped the size from the caller to the known size of the buffer. Do that using min_t(). Reported-by: Bagas Sanjaya <bagasdotme@gmail.com> Closes: https://lore.kernel.org/linuxppc-dev/YpbUcPrm61RLIiZF@debian.me/ Reported-by: Jan-Benedict Glaw <jbglaw@lug-owl.de> Closes: https://lore.kernel.org/linuxppc-dev/20221212215117.aa7255t7qd6yefk4@lug-owl.de/ Reported-by: "Gustavo A. R. Silva" <gustavo@embeddedor.com> Closes: https://lore.kernel.org/linuxppc-dev/6a8bf78c-aedb-4d5a-b0aa-82a51a17b884@embeddedor.com/ Reviewed-by: "Gustavo A. R. Silva" <gustavoars@kernel.org> Build-tested-by: "Gustavo A. R. Silva" <gustavoars@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231120235436.1569255-1-mpe@ellerman.id.au
2023-11-27powerpc: add crtsavres.o to always-y instead of extra-yMasahiro Yamada
crtsavres.o is linked to modules. However, as explained in commit d0e628cd817f ("kbuild: doc: clarify the difference between extra-y and always-y"), 'make modules' does not build extra-y. For example, the following command fails: $ make ARCH=powerpc LLVM=1 KBUILD_MODPOST_WARN=1 mrproper ps3_defconfig modules [snip] LD [M] arch/powerpc/platforms/cell/spufs/spufs.ko ld.lld: error: cannot open arch/powerpc/lib/crtsavres.o: No such file or directory make[3]: *** [scripts/Makefile.modfinal:56: arch/powerpc/platforms/cell/spufs/spufs.ko] Error 1 make[2]: *** [Makefile:1844: modules] Error 2 make[1]: *** [/home/masahiro/workspace/linux-kbuild/Makefile:350: __build_one_by_one] Error 2 make: *** [Makefile:234: __sub-make] Error 2 Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Fixes: baa25b571a16 ("powerpc/64: Do not link crtsavres.o in vmlinux") Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231120232332.4100288-1-masahiroy@kernel.org
2023-10-23powerpc/code-patching: introduce patch_instructions()Hari Bathini
patch_instruction() entails setting up pte, patching the instruction, clearing the pte and flushing the tlb. If multiple instructions need to be patched, every instruction would have to go through the above drill unnecessarily. Instead, introduce patch_instructions() function that sets up the pte, clears the pte and flushes the tlb only once per page range of instructions to be patched. Duplicate most of the patch_instruction() code instead of merging with it, to avoid the performance degradation observed on ppc32, for patch_instruction(), with the code path merged. Also, setup poking_init() always as BPF expects poking_init() to be setup even when STRICT_KERNEL_RWX is off. Signed-off-by: Hari Bathini <hbathini@linux.ibm.com> Acked-by: Song Liu <song@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231020141358.643575-2-hbathini@linux.ibm.com
2023-10-20powerpc/code-patching: Perform hwsync in __patch_instruction() in case of ↵Christophe Leroy
failure Commit c28c15b6d28a ("powerpc/code-patching: Use temporary mm for Radix MMU") added a hwsync for when __patch_instruction() fails, we results in a quite odd unbalanced logic. Instead of calling mb() when __patch_instruction() returns an error, call mb() in the __patch_instruction()'s error path directly. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/e88b154eaf2efd9ff177d472d3411dcdec8ff4f5.1696675567.git.christophe.leroy@csgroup.eu
2023-10-20powerpc/qspinlock: Rename yield_propagate_owner tunableNicholas Piggin
Rename yield_propagate_owner to yield_sleepy_owner, which better describes what it does (what, not how). Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-7-npiggin@gmail.com
2023-10-20powerpc/qspinlock: Propagate sleepy if previous waiter is preemptedNicholas Piggin
The sleepy (aka lock-owner-is-preempted) condition is propagated down the queue by each waiter. If a waiter becomes preempted, it can no longer propagate sleepy. To allow subsequent waiters to yield to the lock owner, also check the lock owner in this case. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-6-npiggin@gmail.com
2023-10-20powerpc/qspinlock: don't propagate the not-sleepy stateNicholas Piggin
To simplify things, don't propagate the not-sleepy condition back down the queue. Instead, have the waiters clear their own node->sleepy when finding the lock owner is not preempted. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-5-npiggin@gmail.com
2023-10-20powerpc/qspinlock: propagate owner preemptedness rather than CPU numberNicholas Piggin
Rather than propagating the CPU number of the preempted lock owner, just propagate whether the owner was preempted. Waiters must read the lock value when yielding to it to prevent races anyway, so might as well always load the owner CPU from the lock. To further simplify the code, also don't propagate the -1 (or sleepy=false in the new scheme) down the queue. Instead, have the waiters clear it themselves when finding the lock owner is not preempted. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-4-npiggin@gmail.com
2023-10-20powerpc/qspinlock: stop queued waiters trying to set lock sleepyNicholas Piggin
If a queued waiter notices the lock owner or the previous waiter has been preempted, it attempts to mark the lock sleepy, but it does this as a try-set operation using the original lock value it got when queueing, which will become stale as the queue progresses, and the try-set will fail. Drop this and just set the sleepy seen clock. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Reviewed-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-3-npiggin@gmail.com
2023-10-18powerpc/qspinlock: Fix stale propagated yield_cpuNicholas Piggin
yield_cpu is a sample of a preempted lock holder that gets propagated back through the queue. Queued waiters use this to yield to the preempted lock holder without continually sampling the lock word (which would defeat the purpose of MCS queueing by bouncing the cache line). The problem is that yield_cpu can become stale. It can take some time to be passed down the chain, and if any queued waiter gets preempted then it will cease to propagate the yield_cpu to later waiters. This can result in yielding to a CPU that no longer holds the lock, which is bad, but particularly if it is currently in H_CEDE (idle), then it appears to be preempted and some hypervisors (PowerVM) can cause very long H_CONFER latencies waiting for H_CEDE wakeup. This results in latency spikes and hard lockups on oversubscribed partitions with lock contention. This is a minimal fix. Before yielding to yield_cpu, sample the lock word to confirm yield_cpu is still the owner, and bail out of it is not. Thanks to a bunch of people who reported this and tracked down the exact problem using tracepoints and dispatch trace logs. Fixes: 28db61e207ea ("powerpc/qspinlock: allow propagation of yield CPU down the queue") Cc: stable@vger.kernel.org # v6.2+ Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> Reported-by: Laurent Dufour <ldufour@linux.ibm.com> Reported-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Debugged-by: "Nysal Jan K.A" <nysal@linux.ibm.com> Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Tested-by: Shrikanth Hegde <sshegde@linux.vnet.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20231016124305.139923-2-npiggin@gmail.com
2023-08-24powerpc: Drop zalloc_maybe_bootmem()Michael Ellerman
The only callers of zalloc_maybe_bootmem() are PCI setup routines. These used to be called early during boot before slab setup, and also during runtime due to hotplug. But commit 5537fcb319d0 ("powerpc/pci: Add ppc_md.discover_phbs()") moved the boot-time calls later, after slab setup, meaning there's no longer any need for zalloc_maybe_bootmem(), kzalloc() can be used in all cases. Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230823055430.752550-1-mpe@ellerman.id.au
2023-08-16powerpc: replace #include <asm/export.h> with #include <linux/export.h>Masahiro Yamada
Commit ddb5cdbafaaa ("kbuild: generate KSYMTAB entries by modpost") deprecated <asm/export.h>, which is now a wrapper of <linux/export.h>. Replace #include <asm/export.h> with #include <linux/export.h>. After all the <asm/export.h> lines are converted, <asm/export.h> and <asm-generic/export.h> will be removed. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> [mpe: Fixup selftests that stub asm/export.h] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230806150954.394189-2-masahiroy@kernel.org
2023-08-16powerpc/step: Mark __copy_mem_out() and __emulate_dcbz() __always_inlineChristophe Leroy
objtool reports two folliwng warnings: arch/powerpc/lib/sstep.o: warning: objtool: copy_mem_out+0x3c (.text+0x30c): call to __copy_mem_out() with UACCESS enabled arch/powerpc/lib/sstep.o: warning: objtool: emulate_dcbz+0x70 (.text+0x4dc): call to __emulate_dcbz() with UACCESS enabled Mark __copy_mem_out() and __emulate_dcbz() __always_inline Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/f1d4a15da70190f8c2fcddb377bbc1e09827242c.1687343857.git.christophe.leroy@csgroup.eu
2023-08-02powerpc/features: Add capability to update mmu features laterChristophe Leroy
On powerpc32, features fixup is performed very early and that's too early to read the cmdline and take into account 'nosmap' parameter. On the other hand, no userspace access is performed that early and KUAP feature fixup can be performed later. Add a function to update mmu features. The function is passed a mask with the features that can be updated. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/31b27ee2c9d338f4f82cd8cd69d6bff979495290.1689091022.git.christophe.leroy@csgroup.eu
2023-06-27powerpc: remove checks for binutils older than 2.25Masahiro Yamada
Commit e4412739472b ("Documentation: raise minimum supported version of binutils to 2.25") allows us to remove the checks for old binutils. There is no more user for ld-ifversion. Remove it as well. Signed-off-by: Masahiro Yamada <masahiroy@kernel.org> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230119082250.151485-1-masahiroy@kernel.org
2023-06-21powerpc: qspinlock: Enforce qnode writes prior to publishing to queueRohan McLure
Annotate the release barrier and memory clobber (in effect, producing a compiler barrier) in the publish_tail_cpu call. These barriers have the effect of ensuring that qnode attributes are all written to prior to publish the node to the waitqueue. Even while the initial write to the 'locked' attribute is guaranteed to terminate prior to the node being visible, KCSAN still complains that the write is reorderable by the compiler. Issue a kcsan_release() to inform KCSAN of the release barrier contained in publish_tail_cpu(). Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230510033117.1395895-3-rmclure@linux.ibm.com
2023-06-21powerpc: qspinlock: Mark accesses to qnode lock checksRohan McLure
The powerpc implementation of qspinlocks will both poll and spin on the bitlock guarding a qnode. Mark these accesses with READ_ONCE to convey to KCSAN that polling is intentional here. Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Reviewed-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230510033117.1395895-2-rmclure@linux.ibm.com
2023-04-20powerpc/64: vmlinux support building with PCREL addresingNicholas Piggin
PC-Relative or PCREL addressing is an extension to the ELF ABI which uses Power ISA v3.1 PC-relative instructions to calculate addresses, rather than the traditional TOC scheme. Add an option to build vmlinux using pcrel addressing. Modules continue to use TOC addressing. - TOC address helpers and r2 are poisoned with -1 when running vmlinux. r2 could be used for something useful once things are ironed out. - Assembly must call C functions with @notoc annotation, or the linker complains aobut a missing nop after the call. This is done with the CFUNC macro introduced earlier. - Boot: with the exception of prom_init, the execution branches to the kernel virtual address early in boot, before any addresses are generated, which ensures 34-bit pcrel addressing does not miss the high PAGE_OFFSET bits. TOC relative addressing has a similar requirement. prom_init does not go to the virtual address and its addresses should not carry over to the post-prom kernel. - Ftrace trampolines are converted from TOC addressing to pcrel addressing, including module ftrace trampolines that currently use the kernel TOC to find ftrace target functions. - BPF function prologue and function calling generation are converted from TOC to pcrel. - copypage_64.S has an interesting problem, prefixed instructions have alignment restrictions so the linker can add padding, which makes the assembler treat the difference between two local labels as non-constant even if alignment is arranged so padding is not required. This may need toolchain help to solve nicely, for now move the prefix instruction out of the alternate patch section to work around it. This reduces kernel text size by about 6%. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230408021752.862660-6-npiggin@gmail.com
2023-04-20powerpc: add CFUNC assembly label annotationNicholas Piggin
This macro is to be used in assembly where C functions are called. pcrel addressing mode requires branches to functions with a localentry value of 1 to have either a trailing nop or @notoc. This macro permits the latter without changing callers. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> [mpe: Add dummy definitions to fix selftests build] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20230408021752.862660-5-npiggin@gmail.com
2023-03-29powerpc: Remove memcpy_page_flushcache()Ira Weiny
Commit 21b56c847753 ("iov_iter: get rid of separate bvec and xarray callbacks") removed the calls to memcpy_page_flushcache(). Remove the unnecessary memcpy_page_flushcache() call. Signed-off-by: Ira Weiny <ira.weiny@intel.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://msgid.link/20221230-kmap-x86-v1-2-15f1ecccab50@intel.com
2023-02-10powerpc/kcsan: Add exclusions from instrumentationRohan McLure
Exclude various incompatible compilation units from KCSAN instrumentation. Signed-off-by: Rohan McLure <rmclure@linux.ibm.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20230206021801.105268-2-rmclure@linux.ibm.com
2022-12-16powerpc/code-patching: Fix oops with DEBUG_VM enabledMichael Ellerman
Nathan reported that the new per-cpu mm patching oopses if DEBUG_VM is enabled: ------------[ cut here ]------------ kernel BUG at arch/powerpc/mm/pgtable.c:333! Oops: Exception in kernel mode, sig: 5 [#1] LE PAGE_SIZE=64K MMU=Radix SMP NR_CPUS=2048 NUMA PowerNV Modules linked in: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.1.0-rc2+ #1 Hardware name: IBM PowerNV (emulated by qemu) POWER9 0x4e1200 opal:v7.0 PowerNV ... NIP assert_pte_locked+0x180/0x1a0 LR assert_pte_locked+0x170/0x1a0 Call Trace: 0x60000000 (unreliable) patch_instruction+0x618/0x6d0 arch_prepare_kprobe+0xfc/0x2d0 register_kprobe+0x520/0x7c0 arch_init_kprobes+0x28/0x3c init_kprobes+0x108/0x184 do_one_initcall+0x60/0x2e0 kernel_init_freeable+0x1f0/0x3e0 kernel_init+0x34/0x1d0 ret_from_kernel_thread+0x5c/0x64 It's caused by the assert_spin_locked() failing in assert_pte_locked(). The assert fails because the PTE was unlocked in text_area_cpu_up_mm(), and never relocked. The PTE page shouldn't be freed, the patching_mm is only used for patching on this CPU, only that single PTE is ever mapped, and it's only unmapped at CPU offline. In fact assert_pte_locked() has a special case to ignore init_mm entirely, and the patching_mm is more-or-less like init_mm, so possibly the check could be skipped for patching_mm too. But for now be conservative, and use the proper PTE accessors at patching time, so that the PTE lock is held while the PTE is used. That also avoids the warning in assert_pte_locked(). With that it's no longer necessary to save the PTE in cpu_patching_context for the mm_patch_enabled() case. Fixes: c28c15b6d28a ("powerpc/code-patching: Use temporary mm for Radix MMU") Reported-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221216125913.990972-1-mpe@ellerman.id.au
2022-12-12powerpc/qspinlock: Fix 32-bit buildNicholas Piggin
Some 32-bit configurations don't pull in the spin_begin/end/relax definitions. Fix is to restore a lost include. Reported-by: kernel test robot <lkp@intel.com> Fixes: 84990b169557 ("powerpc/qspinlock: add mcs queueing for contended waiters") Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/oe-kbuild-all/202212050224.i7uh9fOh-lkp@intel.com Link: https://lore.kernel.org/r/20221208123225.1566113-1-npiggin@gmail.com
2022-12-02powerpc/code-patching: Remove protection against patching init addresses ↵Christophe Leroy
after init Once init section is freed, attempting to patch init code ends up in the weed. Commit 51c3c62b58b3 ("powerpc: Avoid code patching freed init sections") protected patch_instruction() against that, but it is the responsibility of the caller to ensure that the patched memory is valid. All callers have now been verified and fixed so the check can be removed. This improves ftrace activation by about 2% on 8xx. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/504310828f473d424e2ed229eff57bf075f52796.1669969781.git.christophe.leroy@csgroup.eu
2022-12-02powerpc/feature-fixups: Do not patch init section after initChristophe Leroy
Once init section is freed, attempting to patch init code ends up in the weed. Commit 51c3c62b58b3 ("powerpc: Avoid code patching freed init sections") protected patch_instruction() against that, but it is the responsibility of the caller to ensure that the patched memory is valid. In the same spirit as jump_label with its jump_label_can_update() function, add is_fixup_addr_valid() function to skip patching on freed init section. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/8e9311fc1b057e4e6a2a3a0701ebcc74b787affe.1669969781.git.christophe.leroy@csgroup.eu
2022-12-02powerpc/feature-fixups: Refactor other fixups patchingChristophe Leroy
Several fonctions have the same loop for patching instructions. Introduce function do_patch_fixups() to refactor those loops. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/58ab36949c18f94d466fc98d6c085783b0cd474f.1669969781.git.christophe.leroy@csgroup.eu
2022-12-02powerpc/feature-fixups: Refactor entry fixups patchingChristophe Leroy
Several fonctions have the same loop for patching instructions. Introduce function do_patch_entry_fixups() to refactor those loops. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/79eeff7b20a98f7136da5f79b1f7c436928f27f3.1669969781.git.christophe.leroy@csgroup.eu
2022-12-02powerpc/code-patching: Remove #ifdef CONFIG_STRICT_KERNEL_RWXChristophe Leroy
No need to have one implementation of patch_instruction() for CONFIG_STRICT_KERNEL_RWX and one for !CONFIG_STRICT_KERNEL_RWX. In patch_instruction(), call raw_patch_instruction() when !CONFIG_STRICT_KERNEL_RWX. In poking_init(), bail out immediately, it will be equivalent to the weak default implementation. Everything else is declared static and will be discarded by GCC when !CONFIG_STRICT_KERNEL_RWX. Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/f67d2a109404d03e8fdf1ea15388c8778337a76b.1669969781.git.christophe.leroy@csgroup.eu
2022-12-02Merge branch 'topic/qspinlock' into nextMichael Ellerman
Merge Nick's powerpc qspinlock implementation. From his cover letter: This replaces the generic queued spinlock code (like s390 does) with our own implementation. Generic PV qspinlock code is causing latency / starvation regressions on large systems that are resulting in hard lockups reported (mostly in pathoogical cases). The generic qspinlock code has a number of issues important for powerpc hardware and hypervisors that aren't easily solved without changing code that would impact other architectures. Follow s390's lead and implement our own for now. Issues for powerpc using generic qspinlocks: - The previous lock value should not be loaded with simple loads, and need not be passed around from previous loads or cmpxchg results, because powerpc uses ll/sc-style atomics which can perform more complex operations that do not require this. powerpc implementations tend to prefer loads use larx for improved coherency performance. - The queueing process should absolutely minimise the number of stores to the lock word to reduce exclusive coherency probes, important for large system scalability. The pending logic is counter productive here. - Non-atomic unlock for paravirt locks is important (atomic instructions tend to still be more expensive than x86 CPUs). - Yielding to the lock owner is important in the oversubscribed paravirt case, which requires storing the owner CPU in the lock word. - More control of lock stealing for the paravirt case is important to keep latency down on large systems. - The lock acquisition operation should always be made with a special variant of atomic instructions with the lock hint bit set, including (especially) in the queueing paths. This is more a matter of adding more arch lock helpers so not an insurmountable problem for generic code.
2022-12-02powerpc: add definition for pt_regs offset within an interrupt frameNicholas Piggin
This is a common offset that currently uses the overloaded STACK_FRAME_OVERHEAD constant. It's easier to read and more flexible to use a specific regs offset for this. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221127124942.1665522-8-npiggin@gmail.com
2022-12-02powerpc/code-patching: Consolidate and cache per-cpu patching contextBenjamin Gray
With the temp mm context support, there are CPU local variables to hold the patch address and pte. Use these in the non-temp mm path as well instead of adding a level of indirection through the text_poke_area vm_struct and pointer chasing the pte. As both paths use these fields now, there is no need to let unreferenced variables be dropped by the compiler, so it is cleaner to merge them into a single context struct. This has the additional benefit of removing a redundant CPU local pointer, as only one of cpu_patching_mm / text_poke_area is ever used, while remaining well-typed. It also groups each CPU's data into a single cacheline. Signed-off-by: Benjamin Gray <bgray@linux.ibm.com> [mpe: Shorten name to 'area' as suggested by Christophe] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221109045112.187069-10-bgray@linux.ibm.com
2022-12-02powerpc/code-patching: Use temporary mm for Radix MMUChristopher M. Riedl
x86 supports the notion of a temporary mm which restricts access to temporary PTEs to a single CPU. A temporary mm is useful for situations where a CPU needs to perform sensitive operations (such as patching a STRICT_KERNEL_RWX kernel) requiring temporary mappings without exposing said mappings to other CPUs. Another benefit is that other CPU TLBs do not need to be flushed when the temporary mm is torn down. Mappings in the temporary mm can be set in the userspace portion of the address-space. Interrupts must be disabled while the temporary mm is in use. HW breakpoints, which may have been set by userspace as watchpoints on addresses now within the temporary mm, are saved and disabled when loading the temporary mm. The HW breakpoints are restored when unloading the temporary mm. All HW breakpoints are indiscriminately disabled while the temporary mm is in use - this may include breakpoints set by perf. Use the `poking_init` init hook to prepare a temporary mm and patching address. Initialize the temporary mm using mm_alloc(). Choose a randomized patching address inside the temporary mm userspace address space. The patching address is randomized between PAGE_SIZE and DEFAULT_MAP_WINDOW-PAGE_SIZE. Bits of entropy with 64K page size on BOOK3S_64: bits of entropy = log2(DEFAULT_MAP_WINDOW_USER64 / PAGE_SIZE) PAGE_SIZE=64K, DEFAULT_MAP_WINDOW_USER64=128TB bits of entropy = log2(128TB / 64K) bits of entropy = 31 The upper limit is DEFAULT_MAP_WINDOW due to how the Book3s64 Hash MMU operates - by default the space above DEFAULT_MAP_WINDOW is not available. Currently the Hash MMU does not use a temporary mm so technically this upper limit isn't necessary; however, a larger randomization range does not further "harden" this overall approach and future work may introduce patching with a temporary mm on Hash as well. Randomization occurs only once during initialization for each CPU as it comes online. The patching page is mapped with PAGE_KERNEL to set EAA[0] for the PTE which ignores the AMR (so no need to unlock/lock KUAP) according to PowerISA v3.0b Figure 35 on Radix. Based on x86 implementation: commit 4fc19708b165 ("x86/alternatives: Initialize temporary mm for patching") and: commit b3fd8e83ada0 ("x86/alternatives: Use temporary mm for text poking") From: Benjamin Gray <bgray@linux.ibm.com> Synchronisation is done according to ISA 3.1B Book 3 Chapter 13 "Synchronization Requirements for Context Alterations". Switching the mm is a change to the PID, which requires a CSI before and after the change, and a hwsync between the last instruction that performs address translation for an associated storage access. Instruction fetch is an associated storage access, but the instruction address mappings are not being changed, so it should not matter which context they use. We must still perform a hwsync to guard arbitrary prior code that may have accessed a userspace address. TLB invalidation is local and VA specific. Local because only this core used the patching mm, and VA specific because we only care that the writable mapping is purged. Leaving the other mappings intact is more efficient, especially when performing many code patches in a row (e.g., as ftrace would). Signed-off-by: Christopher M. Riedl <cmr@bluescreens.de> Signed-off-by: Benjamin Gray <bgray@linux.ibm.com> [mpe: Use mm_alloc() per 107b6828a7cd ("x86/mm: Use mm_alloc() in poking_init()")] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221109045112.187069-9-bgray@linux.ibm.com
2022-12-02powerpc/qspinlock: add compile-time tuning adjustmentsNicholas Piggin
This adds compile-time options that allow the EH lock hint bit to be enabled or disabled, and adds some new options that may or may not help matters. To help with experimentation and tuning. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-18-npiggin@gmail.com
2022-12-02powerpc/qspinlock: provide accounting and options for sleepy locksNicholas Piggin
Finding the owner or a queued waiter on a lock with a preempted vcpu is indicative of an oversubscribed guest causing the lock to get into trouble. Provide some options to detect this situation and have new CPUs avoid queueing for a longer time (more steal iterations) to minimise the problems caused by vcpu preemption on the queue. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-17-npiggin@gmail.com
2022-12-02powerpc/qspinlock: allow indefinite spinning on a preempted ownerNicholas Piggin
Provide an option that holds off queueing indefinitely while the lock owner is preempted. This could reduce queueing latencies for very overcommitted vcpu situations. This is disabled by default. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-16-npiggin@gmail.com
2022-12-02powerpc/qspinlock: reduce remote node steal spinsNicholas Piggin
Allow for a reduction in the number of times a CPU from a different node than the owner can attempt to steal the lock before queueing. This could bias the transfer behaviour of the lock across the machine and reduce NUMA crossings. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-15-npiggin@gmail.com
2022-12-02powerpc/qspinlock: use spin_begin/end APINicholas Piggin
Use the spin_begin/spin_cpu_relax/spin_end APIs in qspinlock, which helps to prevent threads issuing a lot of expensive priority nops which may not have much effect due to immediately executing low then medium priority. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-14-npiggin@gmail.com
2022-12-02powerpc/qspinlock: allow lock stealing in trylock and lock fastpathNicholas Piggin
This change allows trylock to steal the lock. It also allows the initial lock attempt to steal the lock rather than bailing out and going to the slow path. This gives trylock more strength: without this a continually-contended lock will never permit a trylock to succeed. With this change, the trylock has a small but non-zero chance. It also gives the lock fastpath most of the benefit of passing the reservation back through to the steal loop in the slow path without the complexity. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-13-npiggin@gmail.com
2022-12-02powerpc/qspinlock: add ability to prod new queue head CPUNicholas Piggin
After the head of the queue acquires the lock, it releases the next waiter in the queue to become the new head. Add an option to prod the new head if its vCPU was preempted. This may only have an effect if queue waiters are yielding. Disable this option by default for now, i.e., no logical change. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-12-npiggin@gmail.com
2022-12-02powerpc/qspinlock: allow propagation of yield CPU down the queueNicholas Piggin
Having all CPUs poll the lock word for the owner CPU that should be yielded to defeats most of the purpose of using MCS queueing for scalability. Yet it may be desirable for queued waiters to yield to a preempted owner. With this change, queue waiters never sample the owner CPU directly from the lock word. The queue head (which is spinning on the lock) propagates the owner CPU back to the next waiter if it finds the owner has been preempted. That waiter then propagates the owner CPU back to the next waiter, and so on. s390 addresses this problem differenty, by having queued waiters sample the lock word to find the owner at a low frequency. That has the advantage of being simpler, the advantage of propagation is that the lock word never has to be accesed by queued waiters, and the transfer of cache lines to transmit the owner data is only required when lock holder vCPU preemption occurs. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-11-npiggin@gmail.com
2022-12-02powerpc/qspinlock: allow stealing when head of queue yieldsNicholas Piggin
If the head of queue is preventing stealing but it finds the owner vCPU is preempted, it will yield its cycles to the owner which could cause it to become preempted. Add an option to re-allow stealers before yielding, and disallow them again after returning from the yield. Disable this option by default for now, i.e., no logical change. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-10-npiggin@gmail.com
2022-12-02powerpc/qspinlock: implement option to yield to previous nodeNicholas Piggin
Queued waiters which are not at the head of the queue don't spin on the lock word but their qnode lock word, waiting for the previous queued CPU to release them. Add an option which allows these waiters to yield to the previous CPU if its vCPU is preempted. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-9-npiggin@gmail.com
2022-12-02powerpc/qspinlock: paravirt yield to lock ownerNicholas Piggin
Waiters spinning on the lock word should yield to the lock owner if the vCPU is preempted. This improves performance when the hypervisor has oversubscribed physical CPUs. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-8-npiggin@gmail.com
2022-12-02powerpc/qspinlock: store owner CPU in lock wordNicholas Piggin
Store the owner CPU number in the lock word so it may be yielded to, as powerpc's paravirtualised simple spinlocks do. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-7-npiggin@gmail.com
2022-12-02powerpc/qspinlock: theft prevention to control latencyNicholas Piggin
Give the queue head the ability to stop stealers. After a number of spins without successfully acquiring the lock, the queue head sets this, which halts stealing and will assure it is the next owner. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-6-npiggin@gmail.com
2022-12-02powerpc/qspinlock: allow new waiters to steal the lock before queueingNicholas Piggin
Allow new waiters to "steal" the lock before queueing. That is, to acquire it while other CPUs have queued. This particularly helps paravirt performance when physical CPUs are oversubscribed, by keeping the lock from becoming a strict FIFO and vCPU preemption causing queue train wrecks. The new __queued_spin_trylock_steal() function is put in qspinlock.h to save having to move it, because it will be used there by a later change. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-5-npiggin@gmail.com
2022-12-02powerpc/qspinlock: convert atomic operations to assemblyNicholas Piggin
This uses more optimal ll/sc style access patterns (rather than cmpxchg), and also sets the EH=1 lock hint on those operations which acquire ownership of the lock. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-4-npiggin@gmail.com
2022-12-02powerpc/qspinlock: add mcs queueing for contended waitersNicholas Piggin
This forms the basis of the qspinlock slow path. Like generic qspinlocks and unlike the vanilla MCS algorithm, the lock owner does not participate in the queue, only waiters. The first waiter spins on the lock word, then when the lock is released it takes ownership and unqueues the next waiter. This is how qspinlocks can be implemented with the spinlock API -- lock owners don't need a node, only waiters do. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20221126095932.1234527-2-npiggin@gmail.com
2022-12-02powerpc/qspinlock: powerpc qspinlock implementationNicholas Piggin
Add a powerpc specific implementation of queued spinlocks. This is the build framework with a very simple (non-queued) spinlock implementation to begin with. Later changes add queueing, and other features and optimisations one-at-a-time. It is done this way to more easily see how the queued spinlocks are built, and to make performance and correctness bisects more useful. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> [mpe: Drop paravirt.h & processor.h changes to fix 32-bit build] [mpe: Fix 32-bit build of qspinlock.o & disallow GENERIC_LOCKBREAK per Nick] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/CONLLQB6DCJU.2ZPOS7T6S5GRR@bobo
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