From dea0d5a2fde62237ff14c41cb05dd151cebf84c0 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
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 <yujie.liu@intel.com>
Link: https://lore.kernel.org/r/202209301338.aca913c3-yujie.liu@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220930230008.1636044-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
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 9cf1ba865562e..104b72df33d6a 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:
--
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