2017-06-05 20:07 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: > > > 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; > You are right. Regards, Wanpeng Li
