linux-kernel - Re: [PATCH v2 3/5] KVM: selftests: aarch64: Fix the buggy [enable|disable]

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Message-ID: <b3882f12-04e0-4293-9f94-19895b182d2f@redhat.com>
Date:   Thu, 14 Dec 2023 11:13:38 +0100
From:   Eric Auger <eauger@...hat.com>
To:     Shaoqin Huang <shahuang@...hat.com>, Marc Zyngier <maz@...nel.org>,
        Oliver Upton <oliver.upton@...ux.dev>, kvmarm@...ts.linux.dev
Cc:     James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Shuah Khan <shuah@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, kvm@...r.kernel.org,
        linux-kselftest@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/5] KVM: selftests: aarch64: Fix the buggy
 [enable|disable]_counter

Hi Shaoqin,

On 11/29/23 08:27, Shaoqin Huang wrote:
> In general, the set/clr registers should always be used in their
> write form, never in a RMW form (imagine an interrupt disabling
> a counter between the read and the write...).
> 
> The current implementation of [enable|disable]_counter both use the RMW
> form, fix them by directly write to the set/clr registers.
> 
> At the same time, it also fix the buggy disable_counter() which would
> end up disabling all the counters.
> 
> Signed-off-by: Shaoqin Huang <shahuang@...hat.com>
Reviewed-by: Eric Auger <eric.auger@...hat.com>

Eric

> ---
>  tools/testing/selftests/kvm/include/aarch64/vpmu.h | 8 ++------
>  1 file changed, 2 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/include/aarch64/vpmu.h b/tools/testing/selftests/kvm/include/aarch64/vpmu.h
> index e0cc1ca1c4b7..644dae3814b5 100644
> --- a/tools/testing/selftests/kvm/include/aarch64/vpmu.h
> +++ b/tools/testing/selftests/kvm/include/aarch64/vpmu.h
> @@ -78,17 +78,13 @@ static inline void write_sel_evtyper(int sel, unsigned long val)
>  
>  static inline void enable_counter(int idx)
>  {
> -	uint64_t v = read_sysreg(pmcntenset_el0);
> -
> -	write_sysreg(BIT(idx) | v, pmcntenset_el0);
> +	write_sysreg(BIT(idx), pmcntenset_el0);
>  	isb();
>  }
>  
>  static inline void disable_counter(int idx)
>  {
> -	uint64_t v = read_sysreg(pmcntenset_el0);
> -
> -	write_sysreg(BIT(idx) | v, pmcntenclr_el0);
> +	write_sysreg(BIT(idx), pmcntenclr_el0);
>  	isb();
>  }
>