Re: [PATCH 4/8] x86/cpufeatures: Add PerfCtrVirt feature bit

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] The patch modifies `arch/x86/include/asm/cpufeatures.h` but fails to update its synchronized copy in `tools/arch/x86/include/asm/cpufeatures.h`.
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--- Patch [4]: [PATCH 4/8] x86/cpufeatures: Add PerfCtrVirt feature bit ---
commit d0af0746d5778097e8c3fa7f7763e5d0b909732c
Author: Sandipan Das <sandipan.das@amd.com>

x86/cpufeatures: Add PerfCtrVirt feature bit

This commit defines a feature flag for bit 8 of CPUID leaf 0x8000000A EDX
which indicates support for PMC virtualization. Hypervisors can use this
feature to offload the guest PMU context switch to hardware. This enables
hardware-switched mediated PMU in KVM.

> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 1b4a48bff18f7..d6281870efe02 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -374,6 +374,7 @@
>  #define X86_FEATURE_VMCBCLEAN		(15*32+ 5) /* "vmcb_clean" VMCB clean bits support */
>  #define X86_FEATURE_FLUSHBYASID		(15*32+ 6) /* "flushbyasid" Flush-by-ASID support */
>  #define X86_FEATURE_DECODEASSISTS	(15*32+ 7) /* "decodeassists" Decode Assists support */
> +#define X86_FEATURE_PERFCTR_VIRT	(15*32+ 8) /* PMC virtualization support */

[Severity: Low]
Should this addition also be mirrored in the tools directory?

When arch/x86/include/asm/cpufeatures.h is modified, it usually requires a
synchronized update in tools/arch/x86/include/asm/cpufeatures.h.

Does omitting this update trigger a kernel ABI header differences warning
from check-headers.sh during the tools/perf build?

>  #define X86_FEATURE_PAUSEFILTER		(15*32+10) /* "pausefilter" Filtered pause intercept */
>  #define X86_FEATURE_PFTHRESHOLD		(15*32+12) /* "pfthreshold" Pause filter threshold */
>  #define X86_FEATURE_AVIC		(15*32+13) /* "avic" Virtual Interrupt Controller */

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Sashiko AI review · https://sashiko.dev/#/patchset/cover.1786345201.git.sandipan.das@amd.com?part=4