From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave.Martin@arm.com (Dave Martin) Date: Thu, 14 Jun 2018 12:42:26 +0100 Subject: [PATCH 4/4] KVM: arm64: Avoid mistaken attempts to save SVE state for vcpus In-Reply-To: <1528976546-25999-1-git-send-email-Dave.Martin@arm.com> References: <1528976039-25826-1-git-send-email-Dave.Martin@arm.com> <1528976546-25999-1-git-send-email-Dave.Martin@arm.com> Message-ID: <1528976546-25999-4-git-send-email-Dave.Martin@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Commit e6b673b ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") uses fpsimd_save() to save the FPSIMD state for a vcpu when scheduling the vcpu out. However, currently current's value of TIF_SVE is restored before calling fpsimd_save() which means that fpsimd_save() may erroneously attempt to save SVE state from the vcpu. This enables current's vector state to be polluted with guest data. current->thread.sve_state may be unallocated or not large enough, so this can also trigger a NULL dereference or buffer overrun. Instead of this, TIF_SVE should be configured properly for the guest when calling fpsimd_save() with the vcpu context loaded. This patch ensures this my delaying restoration of current's TIF_SVE until after the call to fpsimd_save(). Fixes: e6b673b741ea ("KVM: arm64: Optimise FPSIMD handling to reduce guest/host thrashing") Signed-off-by: Dave Martin --- arch/arm64/kvm/fpsimd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/arch/arm64/kvm/fpsimd.c b/arch/arm64/kvm/fpsimd.c index 30c7a34..4aaf78e 100644 --- a/arch/arm64/kvm/fpsimd.c +++ b/arch/arm64/kvm/fpsimd.c @@ -99,9 +99,6 @@ void kvm_arch_vcpu_ctxsync_fp(struct kvm_vcpu *vcpu) */ static void __kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) { - update_thread_flag(TIF_SVE, - vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE); - if (vcpu->arch.flags & KVM_ARM64_FP_ENABLED) { /* Clean guest FP state to memory and invalidate cpu view */ fpsimd_save(); @@ -119,6 +116,9 @@ static void __kvm_arch_vcpu_put_fp(struct kvm_vcpu *vcpu) else sysreg_clear_set(CPACR_EL1, CPACR_EL1_ZEN_EL0EN, 0); } + + update_thread_flag(TIF_SVE, + vcpu->arch.flags & KVM_ARM64_HOST_SVE_IN_USE); } -- 2.1.4