linux-kernel - Re: [PATCH v4 06/15] RISC-V: KVM: No need to update the counter value during reset

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Message-ID: <20240302-a82f4ba5d90bc3d85f3ed83b@orel>
Date: Sat, 2 Mar 2024 08:47:33 +0100
From: Andrew Jones <ajones@...tanamicro.com>
To: Atish Patra <atishp@...osinc.com>
Cc: linux-kernel@...r.kernel.org, Anup Patel <anup@...infault.org>, 
	Albert Ou <aou@...s.berkeley.edu>, Alexandre Ghiti <alexghiti@...osinc.com>, 
	Atish Patra <atishp@...shpatra.org>, Conor Dooley <conor.dooley@...rochip.com>, 
	Guo Ren <guoren@...nel.org>, Icenowy Zheng <uwu@...nowy.me>, kvm-riscv@...ts.infradead.org, 
	kvm@...r.kernel.org, linux-kselftest@...r.kernel.org, linux-riscv@...ts.infradead.org, 
	Mark Rutland <mark.rutland@....com>, Palmer Dabbelt <palmer@...belt.com>, 
	Paolo Bonzini <pbonzini@...hat.com>, Paul Walmsley <paul.walmsley@...ive.com>, 
	Shuah Khan <shuah@...nel.org>, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v4 06/15] RISC-V: KVM: No need to update the counter
 value during reset

On Wed, Feb 28, 2024 at 05:01:21PM -0800, Atish Patra wrote:
> The virtual counter value is updated during pmu_ctr_read. There is no need
> to update it in reset case. Otherwise, it will be counted twice which is
> incorrect.
> 
> Fixes: 0cb74b65d2e5 ("RISC-V: KVM: Implement perf support without sampling")
> Reviewed-by: Anup Patel <anup@...infault.org>
> Signed-off-by: Atish Patra <atishp@...osinc.com>
> ---
>  arch/riscv/kvm/vcpu_pmu.c | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/riscv/kvm/vcpu_pmu.c b/arch/riscv/kvm/vcpu_pmu.c
> index 86391a5061dd..b1574c043f77 100644
> --- a/arch/riscv/kvm/vcpu_pmu.c
> +++ b/arch/riscv/kvm/vcpu_pmu.c
> @@ -397,7 +397,6 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
>  {
>  	struct kvm_pmu *kvpmu = vcpu_to_pmu(vcpu);
>  	int i, pmc_index, sbiret = 0;
> -	u64 enabled, running;
>  	struct kvm_pmc *pmc;
>  	int fevent_code;
>  
> @@ -432,12 +431,9 @@ int kvm_riscv_vcpu_pmu_ctr_stop(struct kvm_vcpu *vcpu, unsigned long ctr_base,
>  				sbiret = SBI_ERR_ALREADY_STOPPED;
>  			}
>  
> -			if (flags & SBI_PMU_STOP_FLAG_RESET) {
> -				/* Relase the counter if this is a reset request */
> -				pmc->counter_val += perf_event_read_value(pmc->perf_event,
> -									  &enabled, &running);
> +			if (flags & SBI_PMU_STOP_FLAG_RESET)
> +				/* Release the counter if this is a reset request */
>  				kvm_pmu_release_perf_event(pmc);
> -			}
>  		} else {
>  			sbiret = SBI_ERR_INVALID_PARAM;
>  		}
> -- 
> 2.34.1
>

Reviewed-by: Andrew Jones <ajones@...tanamicro.com>