KVM: arm64: Always start with clearing SVE flag on load

[ 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@kernel.org>
Cc: stable@vger.kernel.org
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220528113829.1043361-2-maz@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 2d15e1d6e2141b25edf97a5426a139353eacee48..24734bfcfaa00f3ace45dacfbc09cf6e91923821 100644 (file)
--- 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;
 }