RE: Implement generic double fault generation mechanism

["Dong, Eddie" <eddie.dong@xxxxxxxxx>]

Gleb Natapov wrote:
>> +
>> +static int exception_class(int vector)
>> +{
>> +	if (vector == 14)
>> +		return EXCPT_PF;
>> +	else if (vector == 0 || (vector >= 10 && vector <= 13)) +		return
>> EXCPT_CONTRIBUTORY; +	else
>> +		return EXCPT_BENIGN;
>> +}
>> +
> This makes double fault (8) benign exception. Surely not what you
> want. 

double fault fall into neither of above class per SDM. But it should be 
checked earlier than generating DB fault. See new updated.
>> +	/* to check exception */
>> +	prev_nr = vcpu->arch.exception.nr;
>> +	class2 = exception_class(nr);
>> +	class1 = exception_class(prev_nr);
>> +	if ((class1 == EXCPT_CONTRIBUTORY && class2 == EXCPT_CONTRIBUTORY)
>> +		|| (class1 == EXCPT_PF && class2 != EXCPT_BENIGN)) {
>> +		/* generate double fault per SDM Table 5-5 */
>> +		printk(KERN_DEBUG "kvm: double fault 0x%x on 0x%x\n",
>> +			prev_nr, nr); +		vcpu->arch.exception.pending = true;
>> +		vcpu->arch.exception.has_error_code = 1;
>> +		vcpu->arch.exception.nr = DF_VECTOR;
>> +		vcpu->arch.exception.error_code = 0;
>> +		if (prev_nr == DF_VECTOR) {
>> +			/* triple fault -> shutdown */
>> +			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests); +		}
>> +	} else
>> +		printk(KERN_ERR "Exception 0x%x on 0x%x happens serially\n",
>> +			prev_nr, nr); +}
> When two exceptions happens serially is is better to replace pending
> exception with a new one. This way the first exception (that is lost)
> will be regenerated when instruction will be re-executed.

Do you want it to be covered for now? For exception, it is easy but for IRQ, it needs to be pushed back.

Thx, eddie



    Move Double-Fault generation logic out of page fault
    exception generating function to cover more generic case.
    
    Signed-off-by: Eddie Dong <eddie.dong@xxxxxxxxx>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index ab1fdac..d0e75a2 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -162,12 +162,60 @@ 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)
+{
+	if (vector == 14)
+		return EXCPT_PF;
+	else if (vector == 0 || (vector >= 10 && vector <= 13))
+		return EXCPT_CONTRIBUTORY;
+	else
+		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) {
+		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 */
+		printk(KERN_DEBUG "kvm: double fault 0x%x on 0x%x\n",
+			prev_nr, nr);
+		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
+		printk(KERN_ERR "Exception 0x%x on 0x%x happens serially\n",
+			prev_nr, nr);
+}
+
 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);
 
@@ -176,18 +224,6 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
 {
 	++vcpu->stat.pf_guest;
 
-	if (vcpu->arch.exception.pending) {
-		if (vcpu->arch.exception.nr == PF_VECTOR) {
-			printk(KERN_DEBUG "kvm: inject_page_fault:"
-					" double fault 0x%lx\n", addr);
-			vcpu->arch.exception.nr = DF_VECTOR;
-			vcpu->arch.exception.error_code = 0;
-		} else if (vcpu->arch.exception.nr == DF_VECTOR) {
-			/* triple fault -> shutdown */
-			set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
-		}
-		return;
-	}
 	vcpu->arch.cr2 = addr;
 	kvm_queue_exception_e(vcpu, PF_VECTOR, error_code);
 }
@@ -200,11 +236,7 @@ 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);

Attachment: irq2.patch
Description: irq2.patch