[PATCH] KVM: SVM: Fix nested VM-Exit on #GP interception handling

[PATCH] KVM: SVM: Fix nested VM-Exit on #GP interception handling

[Sean Christopherson]

Fix the interpreation of nested_svm_vmexit()'s return value when
synthesizing a nested VM-Exit after intercepting an SVM instruction while
L2 was running.  The helper returns '0' on success, whereas a return
value of '0' in the exit handler path means "exit to userspace".  The
incorrect return value causes KVM to exit to userspace without filling
the run state, e.g. QEMU logs "KVM: unknown exit, hardware reason 0".

Fixes: 14c2bf81fcd2 ("KVM: SVM: Fix #GP handling for doubly-nested virtualization")
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/svm/svm.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 14e41dddc7eb..c4f2f2f6b945 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2200,13 +2200,18 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
 		[SVM_INSTR_VMSAVE] = vmsave_interception,
 	};
 	struct vcpu_svm *svm = to_svm(vcpu);
+	int ret;
 
 	if (is_guest_mode(vcpu)) {
 		svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode];
 		svm->vmcb->control.exit_info_1 = 0;
 		svm->vmcb->control.exit_info_2 = 0;
 
-		return nested_svm_vmexit(svm);
+		/* Returns '1' or -errno on failure, '0' on success. */
+		ret = nested_svm_vmexit(svm);
+		if (ret)
+			return ret;
+		return 1;
 	}
 	return svm_instr_handlers[opcode](vcpu);
 }
-- 
2.30.0.617.g56c4b15f3c-goog

Re: [PATCH] KVM: SVM: Fix nested VM-Exit on #GP interception handling

[Paolo Bonzini]

On 24/02/21 01:56, Sean Christopherson wrote:
> Fix the interpreation of nested_svm_vmexit()'s return value when
> synthesizing a nested VM-Exit after intercepting an SVM instruction while
> L2 was running.  The helper returns '0' on success, whereas a return
> value of '0' in the exit handler path means "exit to userspace".  The
> incorrect return value causes KVM to exit to userspace without filling
> the run state, e.g. QEMU logs "KVM: unknown exit, hardware reason 0".
> 
> Fixes: 14c2bf81fcd2 ("KVM: SVM: Fix #GP handling for doubly-nested virtualization")
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
>   arch/x86/kvm/svm/svm.c | 7 ++++++-
>   1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 14e41dddc7eb..c4f2f2f6b945 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -2200,13 +2200,18 @@ static int emulate_svm_instr(struct kvm_vcpu *vcpu, int opcode)
>   		[SVM_INSTR_VMSAVE] = vmsave_interception,
>   	};
>   	struct vcpu_svm *svm = to_svm(vcpu);
> +	int ret;
>   
>   	if (is_guest_mode(vcpu)) {
>   		svm->vmcb->control.exit_code = guest_mode_exit_codes[opcode];
>   		svm->vmcb->control.exit_info_1 = 0;
>   		svm->vmcb->control.exit_info_2 = 0;
>   
> -		return nested_svm_vmexit(svm);
> +		/* Returns '1' or -errno on failure, '0' on success. */
> +		ret = nested_svm_vmexit(svm);
> +		if (ret)
> +			return ret;
> +		return 1;
>   	}
>   	return svm_instr_handlers[opcode](vcpu);
>   }
> 

Queued, thanks.

Paolo