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
