From dea0d5a2fde62237ff14c41cb05dd151cebf84c0 Mon Sep 17 00:00:00 2001 From: Sean Christopherson Date: Fri, 30 Sep 2022 23:00:08 +0000 Subject: [PATCH] KVM: x86: Exempt pending triple fault from event injection sanity check Exempt pending triple faults, a.k.a. KVM_REQ_TRIPLE_FAULT, when asserting that KVM didn't attempt to queue a new exception during event injection. KVM needs to emulate the injection itself when emulating Real Mode due to lack of unrestricted guest support (VMX) and will queue a triple fault if that emulation fails. Ideally the assertion would more precisely filter out the emulated Real Mode triple fault case, but rmode.vm86_active is buried in vcpu_vmx and can't be queried without a new kvm_x86_ops. And unlike "regular" exceptions, triple fault cannot put the vCPU into an infinite loop; the triple fault will force either an exit to userspace or a nested VM-Exit, and triple fault after nested VM-Exit will force an exit to userspace. I.e. there is no functional issue, so just suppress the warning for triple faults. Opportunistically convert the warning to a one-time thing, when it fires, it fires _a lot_, and is usually user triggerable, i.e. can be used to spam the kernel log. Fixes: 7055fb113116 ("KVM: x86: Treat pending TRIPLE_FAULT requests as pending exceptions") Reported-by: kernel test robot Link: https://lore.kernel.org/r/202209301338.aca913c3-yujie.liu@intel.com Signed-off-by: Sean Christopherson Message-Id: <20220930230008.1636044-1-seanjc@google.com> Signed-off-by: Paolo Bonzini --- arch/x86/kvm/x86.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 9cf1ba8..104b72d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10044,7 +10044,20 @@ static int kvm_check_and_inject_events(struct kvm_vcpu *vcpu, kvm_x86_ops.nested_ops->has_events(vcpu)) *req_immediate_exit = true; - WARN_ON(kvm_is_exception_pending(vcpu)); + /* + * KVM must never queue a new exception while injecting an event; KVM + * is done emulating and should only propagate the to-be-injected event + * to the VMCS/VMCB. Queueing a new exception can put the vCPU into an + * infinite loop as KVM will bail from VM-Enter to inject the pending + * exception and start the cycle all over. + * + * Exempt triple faults as they have special handling and won't put the + * vCPU into an infinite loop. Triple fault can be queued when running + * VMX without unrestricted guest, as that requires KVM to emulate Real + * Mode events (see kvm_inject_realmode_interrupt()). + */ + WARN_ON_ONCE(vcpu->arch.exception.pending || + vcpu->arch.exception_vmexit.pending); return 0; out: -- 2.7.4