Why do we expect the VM_EXIT_INTR_INFO and EXIT_QUALIFICATION fields of the VMCS to have the correct values for the injected exception? On Mon, Jun 5, 2017 at 5:19 AM, Wanpeng Li <kernellwp@xxxxxxxxx> wrote: > 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
