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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: 7055fb1131
("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>
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1 changed files with 14 additions and 1 deletions
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@ -10044,7 +10044,20 @@ static int kvm_check_and_inject_events(struct kvm_vcpu *vcpu,
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kvm_x86_ops.nested_ops->has_events(vcpu))
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*req_immediate_exit = true;
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WARN_ON(kvm_is_exception_pending(vcpu));
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/*
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* KVM must never queue a new exception while injecting an event; KVM
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* is done emulating and should only propagate the to-be-injected event
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* to the VMCS/VMCB. Queueing a new exception can put the vCPU into an
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* infinite loop as KVM will bail from VM-Enter to inject the pending
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* exception and start the cycle all over.
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*
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* Exempt triple faults as they have special handling and won't put the
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* vCPU into an infinite loop. Triple fault can be queued when running
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* VMX without unrestricted guest, as that requires KVM to emulate Real
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* Mode events (see kvm_inject_realmode_interrupt()).
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*/
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WARN_ON_ONCE(vcpu->arch.exception.pending ||
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vcpu->arch.exception_vmexit.pending);
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return 0;
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out:
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