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charset="UTF-8" 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 via KVM_SYNC_X86_SREGS is already "broken" as doing so would queue a triple fault for L1 (because "wants_to_run" will be true). Link: https://lore.kernel.org/all/sashiko-outbox-182127@kernel.org Signed-off-by: Sean Christopherson --- 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; -- 2.56.0.385.gac671c819a-goog