From: Sean Christopherson <seanjc@google.com>
To: Sean Christopherson <seanjc@google.com>,
Paolo Bonzini <pbonzini@redhat.com>
Cc: kvm@vger.kernel.org, linux-kernel@vger.kernel.org,
Sashiko Bot <sashiko-bot@kernel.org>
Subject: [PATCH v2 2/6] KVM: x86: Reject clearing EFER.SVME via KVM_SYNC_X86_SREGS if L2 is active
Date: Tue, 27 Oct 2026 15:49:10 -0700 [thread overview]
Message-ID: <20261027224914.1574319-3-seanjc@google.com> (raw)
In-Reply-To: <20261027224914.1574319-1-seanjc@google.com>
Disallow clearing EFER.SVME via KVM_SYNC_X86_SREGS if L2 is active so that
svm_set_efer() can treat yanking the vCPU out of L2 during KVM_RUN as a KVM
bug. Ideally, kvm_is_valid_sregs() itself would reject attempts to clear
SVME while L2 is active, but the risk of breaking userspace, e.g. across
save/restore, is too high. On the other hand, yanking the vCPU out of L2
during save/restore is already "broken" as doing so would queue a triple
fault for L1.
Link: https://lore.kernel.org/all/sashiko-outbox-182127@kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/regs.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kvm/regs.c b/arch/x86/kvm/regs.c
index 3621f1a47d37..e53496fdeb82 100644
--- a/arch/x86/kvm/regs.c
+++ b/arch/x86/kvm/regs.c
@@ -738,6 +738,10 @@ int kvm_run_sync_regs_from_user(struct kvm_vcpu *vcpu)
if (vcpu->run->kvm_dirty_regs & KVM_SYNC_X86_SREGS) {
struct kvm_sregs sregs = vcpu->run->s.regs.sregs;
+ if (is_guest_mode(vcpu) &&
+ (vcpu->arch.efer & EFER_SVME) && !(sregs.efer & EFER_SVME))
+ return -EINVAL;
+
if (__set_sregs(vcpu, &sregs))
return -EINVAL;
--
2.56.0.307.g5fe7bd680c-goog
next prev parent reply other threads:[~2026-10-27 22:49 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-27 22:49 [PATCH v2 0/6] KVM: x86: More EFER.LMA vs. CR4.PAE fixes Sean Christopherson
2026-10-27 22:49 ` [PATCH v2 1/6] Revert "KVM: x86: Skip EFER vs. guest CPUID checks for host-initiated writes" Sean Christopherson
2026-10-27 22:49 ` Sean Christopherson [this message]
2026-10-28 0:08 ` [PATCH v2 2/6] KVM: x86: Reject clearing EFER.SVME via KVM_SYNC_X86_SREGS if L2 is active Yosry Ahmed
2026-10-27 22:49 ` [PATCH v2 3/6] KVM: nSVM: Synthesize #GP instead of SHUTDOWN if L2 attempts to clear EFER.SVME Sean Christopherson
2026-10-27 22:49 ` [PATCH v2 4/6] KVM: x86: Recompute EFER.LMA instead of inheriting the current value on EFER writes Sean Christopherson
2026-10-27 22:49 ` [PATCH v2 5/6] KVM: selftests: Update nSVM EFER test to expect #GP when clearing SVME in L2 Sean Christopherson
2026-10-27 22:49 ` [PATCH v2 6/6] KVM: selftests: Expect failure when trying to set EFER that violates vCPU model Sean Christopherson
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