linux-kernel - Re: [PATCH v9 04/30] arm64/fpsimd: Check enable bit for FA64 when saving EFI state

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Message-ID: <CA+EHjTzDxJsLi315RF43g14psdv44YOuxk6dP6SLgFz4WaY4Hw@mail.gmail.com>
Date: Wed, 7 Jan 2026 19:25:15 +0000
From: Fuad Tabba <tabba@...gle.com>
To: Mark Brown <broonie@...nel.org>
Cc: Marc Zyngier <maz@...nel.org>, Joey Gouly <joey.gouly@....com>, 
	Catalin Marinas <catalin.marinas@....com>, Suzuki K Poulose <suzuki.poulose@....com>, 
	Will Deacon <will@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>, Jonathan Corbet <corbet@....net>, 
	Shuah Khan <shuah@...nel.org>, Oliver Upton <oupton@...nel.org>, Dave Martin <Dave.Martin@....com>, 
	Mark Rutland <mark.rutland@....com>, Ben Horgan <ben.horgan@....com>, 
	linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev, 
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, Peter Maydell <peter.maydell@...aro.org>, 
	Eric Auger <eric.auger@...hat.com>
Subject: Re: [PATCH v9 04/30] arm64/fpsimd: Check enable bit for FA64 when
 saving EFI state

On Tue, 23 Dec 2025 at 01:21, Mark Brown <broonie@...nel.org> wrote:
>
> Currently when deciding if we need to save FFR when in streaming mode prior
> to EFI calls we check if FA64 is supported by the system. Since KVM guest
> support will mean that FA64 might be enabled and disabled at runtime switch
> to checking if traps for FA64 are enabled in SMCR_EL1 instead.
>
> Signed-off-by: Mark Brown <broonie@...nel.org>

Reviewed-by: Fuad Tabba <tabba@...gle.com>

Cheers,
/fuad


> ---
>  arch/arm64/kernel/fpsimd.c | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/kernel/fpsimd.c b/arch/arm64/kernel/fpsimd.c
> index 887fce177c92..f4e8cee00198 100644
> --- a/arch/arm64/kernel/fpsimd.c
> +++ b/arch/arm64/kernel/fpsimd.c
> @@ -1948,6 +1948,11 @@ static bool efi_sm_state;
>   * either doing something wrong or you need to propose some refactoring.
>   */
>
> +static bool fa64_enabled(void)
> +{
> +       return read_sysreg_s(SYS_SMCR_EL1) & SMCR_ELx_FA64;
> +}
> +
>  /*
>   * __efi_fpsimd_begin(): prepare FPSIMD for making an EFI runtime services call
>   */
> @@ -1980,7 +1985,7 @@ void __efi_fpsimd_begin(void)
>                                  * Unless we have FA64 FFR does not
>                                  * exist in streaming mode.
>                                  */
> -                               if (!system_supports_fa64())
> +                               if (!fa64_enabled())
>                                         ffr = !(svcr & SVCR_SM_MASK);
>                         }
>
> @@ -2028,7 +2033,7 @@ void __efi_fpsimd_end(void)
>                                          * Unless we have FA64 FFR does not
>                                          * exist in streaming mode.
>                                          */
> -                                       if (!system_supports_fa64())
> +                                       if (!fa64_enabled())
>                                                 ffr = false;
>                                 }
>                         }
>
> --
> 2.47.3
>