linux-kernel - Re: [PATCH v2] KVM: x86/intr: Explicitly check NMI from guest to eliminate false positives

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Message-ID: <170899198226.3637605.729140637406873438.b4-ty@google.com>
Date: Mon, 26 Feb 2024 18:21:08 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Like Xu <like.xu.linux@...il.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Andi Kleen <ak@...ux.intel.com>, kvm@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] KVM: x86/intr: Explicitly check NMI from guest to
 eliminate false positives

On Wed, 06 Dec 2023 11:20:54 +0800, Like Xu wrote:
> Explicitly checking the source of external interrupt is indeed NMI and not
> other types in the kvm_arch_pmi_in_guest(), which prevents perf-kvm false
> positive samples generated in perf/core NMI mode after vm-exit but before
> kvm_before_interrupt() from being incorrectly labelled as guest samples:
> 
> # test: perf-record + cpu-cycles:HP (which collects host-only precise samples)
> # Symbol                                   Overhead       sys       usr  guest sys  guest usr
> # .......................................  ........  ........  ........  .........  .........
> #
> # Before:
>   [g] entry_SYSCALL_64                       24.63%     0.00%     0.00%     24.63%      0.00%
>   [g] syscall_return_via_sysret              23.23%     0.00%     0.00%     23.23%      0.00%
>   [g] files_lookup_fd_raw                     6.35%     0.00%     0.00%      6.35%      0.00%
> # After:
>   [k] perf_adjust_freq_unthr_context         57.23%    57.23%     0.00%      0.00%      0.00%
>   [k] __vmx_vcpu_run                          4.09%     4.09%     0.00%      0.00%      0.00%
>   [k] vmx_update_host_rsp                     3.17%     3.17%     0.00%      0.00%      0.00%
> 
> [...]

Applied to kvm-x86 pmu, with the !!in_nmi() fixup squashed.  Thanks!

[1/1] KVM: x86/intr: Explicitly check NMI from guest to eliminate false positives
      https://github.com/kvm-x86/linux/commit/812d432373f6

--
https://github.com/kvm-x86/linux/tree/next