Forwarded: [PATCH] KVM: x86: Add debug traces to investigate irq == -1

[syzbot <syzbot+9dcd0a11dc9703a49511@syzkaller.appspotmail.com>]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: [PATCH] KVM: x86: Add debug traces to investigate irq == -1
Author: kartikey406@gmail.com

#syz test: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master


Reported-by: syzbot+9dcd0a11dc9703a49511@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=9dcd0a11dc9703a49511
Signed-off-by: Deepanshu Kartikey <kartikey406@gmail.com>
---
 arch/x86/kvm/i8259.c | 37 ++++++++++++++++++++++++++++++++---
 arch/x86/kvm/irq.c   | 46 +++++++++++++++++++++++++++++++++++++++++---
 2 files changed, 77 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/i8259.c b/arch/x86/kvm/i8259.c
index 6a942ac622d5..4360ed7cc319 100644
--- a/arch/x86/kvm/i8259.c
+++ b/arch/x86/kvm/i8259.c
@@ -233,13 +233,33 @@ int kvm_pic_read_irq(struct kvm *kvm)
 {
 	int irq, irq2, intno;
 	struct kvm_pic *s = kvm->arch.vpic;
-
-	s->output = 0;
-
 	pic_lock(s);
+	printk(KERN_DEBUG
+           "KVM_DEBUG: pic_read_irq START "
+           "output=%d "
+           "IRR0=%02x IMR0=%02x "
+           "ISR0=%02x\n",
+           s->output,
+           s->pics[0].irr,
+           s->pics[0].imr,
+           s->pics[0].isr);
+	s->output = 0;
+	printk(KERN_DEBUG
+           "KVM_DEBUG: output set to 0!\n");
 	irq = pic_get_irq(&s->pics[0]);
+	 printk(KERN_DEBUG
+           "KVM_DEBUG: pic_get_irq returned %d\n",
+           irq);
 	if (irq >= 0) {
 		pic_intack(&s->pics[0], irq);
+		printk(KERN_DEBUG
+               "KVM_DEBUG: after pic_intack "
+               "IRR0=%02x "
+               "ISR0=%02x "
+               "auto_eoi=%d\n",
+               s->pics[0].irr,
+               s->pics[0].isr,
+               s->pics[0].auto_eoi);
 		if (irq == 2) {
 			irq2 = pic_get_irq(&s->pics[1]);
 			if (irq2 >= 0)
@@ -253,6 +273,9 @@ int kvm_pic_read_irq(struct kvm *kvm)
 		} else
 			intno = s->pics[0].irq_base + irq;
 	} else {
+		 printk(KERN_DEBUG
+               "KVM_DEBUG: spurious IRQ! "
+               "no irq found in IRR!\n");
 		/*
 		 * spurious IRQ on host controller
 		 */
@@ -260,6 +283,14 @@ int kvm_pic_read_irq(struct kvm *kvm)
 		intno = s->pics[0].irq_base + irq;
 	}
 	pic_update_irq(s);
+	 printk(KERN_DEBUG
+           "KVM_DEBUG: pic_read_irq END "
+           "intno=%d "
+           "output=%d "
+           "IRR0=%02x\n",
+           intno,
+           s->output,
+           s->pics[0].irr);
 	pic_unlock(s);
 
 	return intno;
diff --git a/arch/x86/kvm/irq.c b/arch/x86/kvm/irq.c
index 8c62c6d4d5c1..1c7541e01d4a 100644
--- a/arch/x86/kvm/irq.c
+++ b/arch/x86/kvm/irq.c
@@ -79,8 +79,19 @@ int kvm_cpu_has_extint(struct kvm_vcpu *v)
 		return 0;
 
 #ifdef CONFIG_KVM_IOAPIC
-	if (pic_in_kernel(v->kvm))
+	if (pic_in_kernel(v->kvm)) {
+		 printk(KERN_DEBUG
+               "KVM_DEBUG: has_extint called "
+               "output=%d "
+               "IRR0=%02x IRR1=%02x "
+               "IMR0=%02x IMR1=%02x\n",
+               v->kvm->arch.vpic->output,
+               v->kvm->arch.vpic->pics[0].irr,
+               v->kvm->arch.vpic->pics[1].irr,
+               v->kvm->arch.vpic->pics[0].imr,
+               v->kvm->arch.vpic->pics[1].imr);
 		return v->kvm->arch.vpic->output;
+	}
 #endif
 
 	WARN_ON_ONCE(!irqchip_split(v->kvm));
@@ -127,7 +138,24 @@ EXPORT_SYMBOL_FOR_KVM_INTERNAL(kvm_cpu_has_interrupt);
  */
 int kvm_cpu_get_extint(struct kvm_vcpu *v)
 {
+	int result;
+	if (pic_in_kernel(v->kvm))
+	 	printk(KERN_DEBUG
+           	       "KVM_DEBUG: get_extint called "
+                       "output=%d\n",
+                       v->kvm->arch.vpic->output);
 	if (!kvm_cpu_has_extint(v)) {
+		if (pic_in_kernel(v->kvm)) {
+		 	printk(KERN_DEBUG
+               		"KVM_DEBUG: has_extint=FALSE "
+               		"returning -1! "
+               		"output=%d\n",
+               		v->kvm->arch.vpic->output);
+		}
+		else
+			printk(KERN_DEBUG
+			       "KVM_DEBUG: has_extint=FALSE "
+                               "no pic in kernel!\n");
 		WARN_ON(!lapic_in_kernel(v));
 		return -1;
 	}
@@ -141,8 +169,20 @@ int kvm_cpu_get_extint(struct kvm_vcpu *v)
 #endif
 
 #ifdef CONFIG_KVM_IOAPIC
-	if (pic_in_kernel(v->kvm))
-		return kvm_pic_read_irq(v->kvm); /* PIC */
+	if (pic_in_kernel(v->kvm)) {
+		 printk(KERN_DEBUG
+               "KVM_DEBUG: calling pic_read_irq "
+               "output=%d\n",
+               v->kvm->arch.vpic->output);
+		result = kvm_pic_read_irq(v->kvm);
+		 printk(KERN_DEBUG
+               "KVM_DEBUG: pic_read_irq returned "
+               "intno=%d "
+               "output=%d\n",
+               result,
+               v->kvm->arch.vpic->output);
+		return result; /* PIC */
+	}
 #endif
 
 	WARN_ON_ONCE(!irqchip_split(v->kvm));
-- 
2.43.0