linux-kernel - [PATCH 5.15 v3 02/11] KVM: arm64: Always start with clearing SVE flag on load

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Message-Id: <20250408-stable-sve-5-15-v3-2-ca9a6b850f55@kernel.org>
Date: Tue, 08 Apr 2025 19:09:57 +0100
From: Mark Brown <broonie@...nel.org>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Marc Zyngier <maz@...nel.org>, James Morse <james.morse@....com>, 
 Suzuki K Poulose <suzuki.poulose@....com>, 
 Catalin Marinas <catalin.marinas@....com>, Will Deacon <will@...nel.org>, 
 Oleg Nesterov <oleg@...hat.com>, Oliver Upton <oliver.upton@...ux.dev>
Cc: linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu, 
 linux-kernel@...r.kernel.org, stable@...r.kernel.org, 
 Mark Brown <broonie@...nel.org>
Subject: [PATCH 5.15 v3 02/11] KVM: arm64: Always start with clearing SVE
 flag on load

From: Marc Zyngier <maz@...nel.org>

[ Upstream commit d52d165d67c5aa26c8c89909003c94a66492d23d ]

On each vcpu load, we set the KVM_ARM64_HOST_SVE_ENABLED
flag if SVE is enabled for EL0 on the host. This is used to restore
the correct state on vpcu put.

However, it appears that nothing ever clears this flag. Once
set, it will stick until the vcpu is destroyed, which has the
potential to spuriously enable SVE for userspace.

We probably never saw the issue because no VMM uses SVE, but
that's still pretty bad. Unconditionally clearing the flag
on vcpu load addresses the issue.

Fixes: 8383741ab2e7 ("KVM: arm64: Get rid of host SVE tracking/saving")
Signed-off-by: Marc Zyngier <maz@...nel.org>
Cc: stable@...r.kernel.org
Reviewed-by: Mark Brown <broonie@...nel.org>
Link: https://lore.kernel.org/r/20220528113829.1043361-2-maz@kernel.org
Signed-off-by: Mark Brown <broonie@...nel.org>
---
 arch/arm64/kvm/fpsimd.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 2d15e1d6e214..24734bfcfaa0 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -75,6 +75,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 	vcpu->arch.flags &= ~KVM_ARM64_FP_ENABLED;
 	vcpu->arch.flags |= KVM_ARM64_FP_HOST;
 
+	vcpu->arch.flags &= ~KVM_ARM64_HOST_SVE_ENABLED;
 	if (read_sysreg(cpacr_el1) & CPACR_EL1_ZEN_EL0EN)
 		vcpu->arch.flags |= KVM_ARM64_HOST_SVE_ENABLED;
 }

-- 
2.39.5