On 03/06/2017 05:21, Wanpeng Li wrote: > Commit 0b6ac343fc (KVM: nVMX: Correct handling of exception injection) mentioned > that "KVM wants to inject page-faults which it got to the guest. This function > assumes it is called with the exit reason in vmcs02 being a #PF exception". > Commit e011c663 (KVM: nVMX: Check all exceptions for intercept during delivery to > L2) allows to check all exceptions for intercept during delivery to L2. However, > there is no guarantee the exit reason is exception currently, when there is an > external interrupt occurred on host, maybe a time interrupt for host which should > not be injected to guest, and somewhere queues an exception, then the function > nested_vmx_check_exception() will be called and the vmexit emulation codes will > try to emulate the "Acknowledge interrupt on exit" behavior, the warning is > triggered. > > This patch fixes it by confirming to inject exception to the guest when the exit > reason in vmcs02 is exception. I am confused. On one hand, the comment originally "this is the only case in which KVM injects a #PF when L2 is running", but I'm not sure it's true. For example, KVM could emulate a movs while running L2. If the source is MMIO and the destination is a missing page, the original failure could be an EPT misconfig, but the access to the destination would cause a #PF in the guest (could be a nice testcase for kvm-unit-tests, BTW :)). On the other hand, why would you reuse to_vmx(vcpu)->exit_reason in nested_vmx_check_exception? Would the following fix the bug: diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c index 9b4b5d6dcd34..ca5d2b93385c 100644 --- a/arch/x86/kvm/vmx.c +++ b/arch/x86/kvm/vmx.c @@ -2425,7 +2425,7 @@ static int nested_vmx_check_exception(struct kvm_vcpu *vcpu, unsigned nr) if (!(vmcs12->exception_bitmap & (1u << nr))) return 0; - nested_vmx_vmexit(vcpu, to_vmx(vcpu)->exit_reason, + nested_vmx_vmexit(vcpu, EXIT_REASON_EXCEPTION_NMI, vmcs_read32(VM_EXIT_INTR_INFO), vmcs_readl(EXIT_QUALIFICATION)); return 1; ? Thanks, Paolo
