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Date: Mon, 18 Mar 2024 22:50:39 +0000
From: Mingwei Zhang <mizhang@google.com>
To: Sean Christopherson <seanjc@google.com>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Namhyung Kim <namhyung@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, Jim Mattson <jmattson@google.com>
Subject: Re: [PATCH 2/3] perf/x86/intel: Expose existence of callback support
 to KVM
Message-ID: <ZfjFP7E0ME5yHJZC@google.com>
References: <20240307011344.835640-1-seanjc@google.com>
 <20240307011344.835640-3-seanjc@google.com>
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In-Reply-To: <20240307011344.835640-3-seanjc@google.com>

On Wed, Mar 06, 2024, Sean Christopherson wrote:
> Add a "has_callstack" field to the x86_pmu_lbr structure used to pass
> information to KVM, and set it accordingly in x86_perf_get_lbr().  KVM
> will use has_callstack to avoid trying to create perf LBR events with
> PERF_SAMPLE_BRANCH_CALL_STACK on CPUs that don't support callstacks.
> 
> Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Mingwei Zhang <mizhang@google.com>
> ---
>  arch/x86/events/intel/lbr.c       | 1 +
>  arch/x86/include/asm/perf_event.h | 1 +
>  2 files changed, 2 insertions(+)
> 
> diff --git a/arch/x86/events/intel/lbr.c b/arch/x86/events/intel/lbr.c
> index 78cd5084104e..4367aa77cb8d 100644
> --- a/arch/x86/events/intel/lbr.c
> +++ b/arch/x86/events/intel/lbr.c
> @@ -1693,6 +1693,7 @@ void x86_perf_get_lbr(struct x86_pmu_lbr *lbr)
>  	lbr->from = x86_pmu.lbr_from;
>  	lbr->to = x86_pmu.lbr_to;
>  	lbr->info = x86_pmu.lbr_info;
> +	lbr->has_callstack = x86_pmu_has_lbr_callstack();
>  }
>  EXPORT_SYMBOL_GPL(x86_perf_get_lbr);
>  
> diff --git a/arch/x86/include/asm/perf_event.h b/arch/x86/include/asm/perf_event.h
> index 3736b8a46c04..7f1e17250546 100644
> --- a/arch/x86/include/asm/perf_event.h
> +++ b/arch/x86/include/asm/perf_event.h
> @@ -555,6 +555,7 @@ struct x86_pmu_lbr {
>  	unsigned int	from;
>  	unsigned int	to;
>  	unsigned int	info;
> +	bool		has_callstack;
>  };
>  
>  extern void perf_get_x86_pmu_capability(struct x86_pmu_capability *cap);
> -- 
> 2.44.0.278.ge034bb2e1d-goog
>