Re: [patch 0/2] Handle multiple exceptions (fixes Win2003 reboot by triple fault)

[Gleb Natapov <gleb@redhat.com>]

> It's actually less readable.  I know 11 is between 10 and 13, but is
> NP_VECTOR between TS_VECTOR and GP_VECTOR?
> 
> This is better as a switch, or even:
> 
> u8 exception_class[] = {
>    [PF_VECTOR] EXPT_PF,
> 
> etc.
OK what about this then:

From: Eddie Dong<eddie.dong@intel.com>

Move Double-Fault generation logic out of page fault
exception generating function to cover more generic case.

Signed-off-by: Eddie Dong<eddie.dong@intel.com>
Signed-off-by: Gleb Natapov<gleb@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 9b0602a..5e95ff9 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -248,12 +248,68 @@ void kvm_set_apic_base(struct kvm_vcpu *vcpu, u64 data)
 }
 EXPORT_SYMBOL_GPL(kvm_set_apic_base);
 
+#define EXCPT_BENIGN		0
+#define EXCPT_CONTRIBUTORY	1
+#define EXCPT_PF		2
+
+static int exception_class(int vector)
+{
+	switch (vector) {
+	case PF_VECTOR:
+		return EXCPT_PF;
+	case DE_VECTOR:
+	case TS_VECTOR:
+	case NP_VECTOR:
+	case SS_VECTOR:
+	case GP_VECTOR:
+		return EXCPT_CONTRIBUTORY;
+	default:
+		break;
+	}
+	return EXCPT_BENIGN;
+}
+
+static void kvm_multiple_exception(struct kvm_vcpu *vcpu,
+		unsigned nr, bool has_error, u32 error_code)
+{
+	u32 prev_nr;
+	int class1, class2;
+
+	if (!vcpu->arch.exception.pending) {
+	queue:
+		vcpu->arch.exception.pending = true;
+		vcpu->arch.exception.has_error_code = has_error;
+		vcpu->arch.exception.nr = nr;
+		vcpu->arch.exception.error_code = error_code;
+		return;
+	}
+
+	/* to check exception */
+	prev_nr = vcpu->arch.exception.nr;
+	if (prev_nr == DF_VECTOR) {
+		/* triple fault -> shutdown */
+		set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
+		return;
+	}
+	class1 = exception_class(prev_nr);
+	class2 = exception_class(nr);
+	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
+		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
+		/* generate double fault per SDM Table 5-5 */
+		vcpu->arch.exception.pending = true;
+		vcpu->arch.exception.has_error_code = true;
+		vcpu->arch.exception.nr = DF_VECTOR;
+		vcpu->arch.exception.error_code = 0;
+	} else
+		/* replace previous exception with a new one in a hope
+		   that instruction re-execution will regenerate lost
+		   exception */
+		goto queue;
+}
+
 void kvm_queue_exception(struct kvm_vcpu *vcpu, unsigned nr)
 {
-	WARN_ON(vcpu->arch.exception.pending);
-	vcpu->arch.exception.pending = true;
-	vcpu->arch.exception.has_error_code = false;
-	vcpu->arch.exception.nr = nr;
+	kvm_multiple_exception(vcpu, nr, false, 0);
 }
 EXPORT_SYMBOL_GPL(kvm_queue_exception);
 
@@ -261,25 +317,6 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
 			   u32 error_code)
 {
 	++vcpu->stat.pf_guest;
-
-	if (vcpu->arch.exception.pending) {
-		switch(vcpu->arch.exception.nr) {
-		case DF_VECTOR:
-			/* triple fault -> shutdown */
-			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
-			return;
-		case PF_VECTOR:
-			vcpu->arch.exception.nr = DF_VECTOR;
-			vcpu->arch.exception.error_code = 0;
-			return;
-		default:
-			/* replace previous exception with a new one in a hope
-			   that instruction re-execution will regenerate lost
-			   exception */
-			vcpu->arch.exception.pending = false;
-			break;
-		}
-	}
 	vcpu->arch.cr2 = addr;
 	kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
 }
@@ -292,11 +329,7 @@ EXPORT_SYMBOL_GPL(kvm_inject_nmi);
 
 void kvm_queue_exception_e(struct kvm_vcpu *vcpu, unsigned nr, u32 error_code)
 {
-	WARN_ON(vcpu->arch.exception.pending);
-	vcpu->arch.exception.pending = true;
-	vcpu->arch.exception.has_error_code = true;
-	vcpu->arch.exception.nr = nr;
-	vcpu->arch.exception.error_code = error_code;
+	kvm_multiple_exception(vcpu, nr, true, error_code);
 }
 EXPORT_SYMBOL_GPL(kvm_queue_exception_e);
 
--
			Gleb.