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

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Message-Id: <20251223-kvm-arm64-sme-v9-4-8be3867cb883@kernel.org>
Date: Tue, 23 Dec 2025 01:20:58 +0000
From: Mark Brown <broonie@...nel.org>
To: 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>
Cc: 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>, Mark Brown <broonie@...nel.org>
Subject: [PATCH v9 04/30] arm64/fpsimd: Check enable bit for FA64 when
 saving EFI state

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;
 				}
 			}

-- 
2.47.3