Re: [PATCH 2/4] KVM: nSVM: propagate the NPF EXITINFO to the guest

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On 09/02/2014 07:46 PM, Paolo Bonzini wrote:
*/
  		if (unlikely(real_gfn == UNMAPPED_GVA))
  			goto error;
@@ -1974,10 +1974,28 @@ static void nested_svm_inject_npf_exit(struct kvm_vcpu *vcpu,
  {
  	struct vcpu_svm *svm = to_svm(vcpu);
- svm->vmcb->control.exit_code = SVM_EXIT_NPF;
-	svm->vmcb->control.exit_code_hi = 0;
-	svm->vmcb->control.exit_info_1 = fault->error_code;
-	svm->vmcb->control.exit_info_2 = fault->address;
+	/*
+	 * We can keep the value that the processor stored in the VMCB,
+	 * but make up something sensible if we hit the WARN.
+	 */
+	if (WARN_ON(svm->vmcb->control.exit_code != SVM_EXIT_NPF)) {
+		svm->vmcb->control.exit_code = SVM_EXIT_NPF;
+		svm->vmcb->control.exit_code_hi = 0;
+		svm->vmcb->control.exit_info_1 = (1ULL << 32);
+		svm->vmcb->control.exit_info_2 = fault->address;
+	}
Its been a while since I looked into this, but is an injected NPF exit
always the result of a real NPF exit?
I think so, but that's why I CCed you. :)

It could always be the result of emulation into which L0 was tricked. I don't think it's a safe assumption.

How about an io-port emulated on
L1 but passed through to L2 by the nested hypervisor. On emulation of
INS or OUTS, KVM would need to read/write to an L2 address space,
It would need to read/write to *L1* (that's where the VMCB's IOIO map
lies), which could result into a regular page fault injected into L1.

Paolo

maybe
causing NPF faults to be injected. In this case an IOIO exit would cause
an injected NPF exit for L1.
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