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* [PATCH] KVM: x86: Return to userspace with internal error on unexpected exit reason
@ 2019-08-26 10:16 Liran Alon
  2019-08-26 10:50 ` Vitaly Kuznetsov
  2019-09-11 13:42 ` Paolo Bonzini
  0 siblings, 2 replies; 4+ messages in thread
From: Liran Alon @ 2019-08-26 10:16 UTC (permalink / raw)
  To: pbonzini, rkrcmar, kvm
  Cc: sean.j.christopherson, jmattson, vkuznets, Liran Alon,
	Mihai Carabas, Nikita Leshenko, Joao Martins

Receiving an unexpected exit reason from hardware should be considered
as a severe bug in KVM. Therefore, instead of just injecting #UD to
guest and ignore it, exit to userspace on internal error so that
it could handle it properly (probably by terminating guest).

In addition, prefer to use vcpu_unimpl() instead of WARN_ONCE()
as handling unexpected exit reason should be a rare unexpected
event (that was expected to never happen) and we prefer to print
a message on it every time it occurs to guest.

Furthermore, dump VMCS/VMCB to dmesg to assist diagnosing such cases.

Reviewed-by: Mihai Carabas <mihai.carabas@oracle.com>
Reviewed-by: Nikita Leshenko <nikita.leshchenko@oracle.com>
Reviewed-by: Joao Martins <joao.m.martins@oracle.com>
Signed-off-by: Liran Alon <liran.alon@oracle.com>
---
 arch/x86/kvm/svm.c       | 11 ++++++++---
 arch/x86/kvm/vmx/vmx.c   |  9 +++++++--
 include/uapi/linux/kvm.h |  2 ++
 3 files changed, 17 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index d685491fce4d..6462c386015d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -5026,9 +5026,14 @@ static int handle_exit(struct kvm_vcpu *vcpu)
 
 	if (exit_code >= ARRAY_SIZE(svm_exit_handlers)
 	    || !svm_exit_handlers[exit_code]) {
-		WARN_ONCE(1, "svm: unexpected exit reason 0x%x\n", exit_code);
-		kvm_queue_exception(vcpu, UD_VECTOR);
-		return 1;
+		vcpu_unimpl(vcpu, "svm: unexpected exit reason 0x%x\n", exit_code);
+		dump_vmcb(vcpu);
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror =
+			KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
+		vcpu->run->internal.ndata = 1;
+		vcpu->run->internal.data[0] = exit_code;
+		return 0;
 	}
 
 	return svm_exit_handlers[exit_code](svm);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 42ed3faa6af8..b5b5b2e5dac5 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -5887,8 +5887,13 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
 	else {
 		vcpu_unimpl(vcpu, "vmx: unexpected exit reason 0x%x\n",
 				exit_reason);
-		kvm_queue_exception(vcpu, UD_VECTOR);
-		return 1;
+		dump_vmcs();
+		vcpu->run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+		vcpu->run->internal.suberror =
+			KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON;
+		vcpu->run->internal.ndata = 1;
+		vcpu->run->internal.data[0] = exit_reason;
+		return 0;
 	}
 }
 
diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 5e3f12d5359e..42070aa5f4e6 100644
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -243,6 +243,8 @@ struct kvm_hyperv_exit {
 #define KVM_INTERNAL_ERROR_SIMUL_EX	2
 /* Encounter unexpected vm-exit due to delivery event. */
 #define KVM_INTERNAL_ERROR_DELIVERY_EV	3
+/* Encounter unexpected vm-exit reason */
+#define KVM_INTERNAL_ERROR_UNEXPECTED_EXIT_REASON	4
 
 /* for KVM_RUN, returned by mmap(vcpu_fd, offset=0) */
 struct kvm_run {
-- 
2.20.1


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2019-08-26 10:16 [PATCH] KVM: x86: Return to userspace with internal error on unexpected exit reason Liran Alon
2019-08-26 10:50 ` Vitaly Kuznetsov
2019-08-26 10:52   ` Liran Alon
2019-09-11 13:42 ` Paolo Bonzini

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