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

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Message-ID: <87343o8jay.fsf@draig.linaro.org>
Date: Thu, 29 Jan 2026 16:39:33 +0000
From: Alex Bennée <alex.bennee@...aro.org>
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>,  Fuad Tabba <tabba@...gle.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

Mark Brown <broonie@...nel.org> writes:

> 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>
> ---
>  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;
>  				}
>  			}

This is conflicting with the now merged 63de2b3859ba1 (arm64/efi: Remove
unneeded SVE/SME fallback preserve/store handling) so I think this patch
can now be dropped?

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro