linux-kernel - [PATCH 5.18 131/141] KVM: arm64: Always start with clearing SVE flag on load

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Date:   Mon, 20 Jun 2022 14:51:09 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Marc Zyngier <maz@...nel.org>,
        Mark Brown <broonie@...nel.org>
Subject: [PATCH 5.18 131/141] KVM: arm64: Always start with clearing SVE flag on load

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

commit d52d165d67c5aa26c8c89909003c94a66492d23d upstream.

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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/arm64/kvm/fpsimd.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -80,6 +80,7 @@ void kvm_arch_vcpu_load_fp(struct kvm_vc
 	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;
 }