linux-kernel - Re: [kvm-unit-tests patch v3 5/8] x86/pmu: Relax precise count check for emulated instructions tests

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Message-ID: <aR-WNu8iFfP1AKBX@google.com>
Date: Thu, 20 Nov 2025 14:29:10 -0800
From: Sean Christopherson <seanjc@...gle.com>
To: Dapeng Mi <dapeng1.mi@...ux.intel.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Jim Mattson <jmattson@...gle.com>, Mingwei Zhang <mizhang@...gle.com>, 
	Zide Chen <zide.chen@...el.com>, Das Sandipan <Sandipan.Das@....com>, 
	Shukla Manali <Manali.Shukla@....com>, Xiaoyao Li <xiaoyao.li@...el.com>, 
	Dapeng Mi <dapeng1.mi@...el.com>
Subject: Re: [kvm-unit-tests patch v3 5/8] x86/pmu: Relax precise count check
 for emulated instructions tests

On Wed, Sep 03, 2025, Dapeng Mi wrote:
> Relax precise count check for emulated instructions tests on these
> platforms with HW overcount issues.
> 
> Signed-off-by: Dapeng Mi <dapeng1.mi@...ux.intel.com>
> ---
>  x86/pmu.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/x86/pmu.c b/x86/pmu.c
> index c54c0988..6bf6eee3 100644
> --- a/x86/pmu.c
> +++ b/x86/pmu.c
> @@ -790,7 +790,7 @@ static void check_emulated_instr(void)
>  
>  	// Check that the end count - start count is at least the expected
>  	// number of instructions and branches.
> -	if (this_cpu_has_perf_global_ctrl()) {
> +	if (this_cpu_has_perf_global_ctrl() && !intel_inst_overcount_flags) {

This skips precise checking if _either_ errata is present.  IIUC, we can still do
a precise check for branches retired on Clearwater Forest, but not for instructions
retired.

>  		report(instr_cnt.count - instr_start == KVM_FEP_INSNS,
>  		       "instruction count");
>  		report(brnch_cnt.count - brnch_start == KVM_FEP_BRANCHES,
> -- 
> 2.34.1
>