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[02/18] KVM: arm64: Always start with clearing SME flag on load

Message ID 20220528113829.1043361-3-maz@kernel.org (mailing list archive)
State New, archived
Headers show
Series KVM/arm64: Refactoring the vcpu flags | expand

Commit Message

Marc Zyngier May 28, 2022, 11:38 a.m. UTC 
On each vcpu load, we set the KVM_ARM64_HOST_SME_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 SME for userspace. As it turns
out, this is due to the SME code being more or less copied from
SVE, and inheriting the same shortcomings.

We never saw the issue because nothing uses SME, and the amount
of testing is probably still pretty low.

Fixes: 861262ab8627 ("KVM: arm64: Handle SME host state when running guests")
Signed-off-by: Marc Zyngier <maz@kernel.org>
---
 arch/arm64/kvm/fpsimd.c | 1 +
 1 file changed, 1 insertion(+)

Comments

Mark Brown May 30, 2022, 2:51 p.m. UTC | #1 
On Sat, May 28, 2022 at 12:38:12PM +0100, Marc Zyngier wrote:
> On each vcpu load, we set the KVM_ARM64_HOST_SME_ENABLED
> flag if SVE is enabled for EL0 on the host. This is used to
> restore the correct state on vpcu put.

s/SVE/SME/

but otherwise

Reviwed-by: Mark Brown <broonie@kernel.org>
diff mbox series

Patch

diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c
index 3c2cfc3adc51..78b3f143a2d0 100644
--- a/arch/arm64/kvm/fpsimd.c
+++ b/arch/arm64/kvm/fpsimd.c
@@ -94,6 +94,7 @@  void kvm_arch_vcpu_load_fp(struct kvm_vcpu *vcpu)
 	 * operations. Do this for ZA as well for now for simplicity.
 	 */
 	if (system_supports_sme()) {
+		vcpu->arch.flags &= ~KVM_ARM64_HOST_SME_ENABLED;
 		if (read_sysreg(cpacr_el1) & CPACR_EL1_SMEN_EL0EN)
 			vcpu->arch.flags |= KVM_ARM64_HOST_SME_ENABLED;