Re: [PATCH v4 03/10] perf/x86/intel: Don't context switch DS_AREA (and PEBS config) if PEBS is unused

[sashiko-bot@kernel.org]

> When filling the list of MSRs to be loaded by KVM on VM-Enter and VM-Exit,
> load the guest values for DS_AREA and (conditionally) MSR_PEBS_DATA_CFG if
> and only if PEBS will be active in the guest, i.e. only if a PEBS record
> may be generated while running the guest.  As shown by the !pebs_ept path,
> it's perfectly safe to run with the host's DS_AREA, so long as PEBS-enabled
> counters are disabled via PERF_GLOBAL_CTRL.
> 
> Omitting DS_AREA and MSR_PEBS_DATA_CFG when PEBS is unused saves two MSR
> writes per MSR on each VMX transition, i.e. eliminates two/four pointless
> MSR writes on each VMX roundtrip when PEBS isn't being used by the guest.
> 
> Fixes: c59a1f106f5c ("KVM: x86/pmu: Add IA32_PEBS_ENABLE MSR emulation for extended PEBS")
> Cc: Jim Mattson <jmattson@google.com>
> Cc: Mingwei Zhang <mizhang@google.com>
> Cc: Stephane Eranian <eranian@google.com>
> Reviewed-by: Jim Mattson <jmattson@google.com>
> Reviewed-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260921191418.950933-1-seanjc@google.com?part=3