KVM: detect if VCPU triple faults

In the current inject_page_fault path KVM only checks if there is another PF
pending and injects a DF then. But it has to check for a pending DF too to
detect a shutdown condition in the VCPU.  If this is not detected the VCPU goes
to a PF -> DF -> PF loop when it should triple fault. This patch detects this
condition and handles it with an KVM_SHUTDOWN exit to userspace.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

2 files changed, 16 insertions, 5 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index dbcff38dfcc3..491eda308289 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -155,11 +155,16 @@ void kvm_inject_page_fault(struct kvm_vcpu *vcpu, unsigned long addr,
                            u32 error_code)
 {
         ++vcpu->stat.pf_guest;
-        if (vcpu->arch.exception.pending && 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;
+        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;
@@ -2676,6 +2681,11 @@ again:
                         r = 0;
                         goto out;
                 }
+                if (test_and_clear_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests)) {
+                        kvm_run->exit_reason = KVM_EXIT_SHUTDOWN;
+                        r = 0;
+                        goto out;
+                }
         }
 
         kvm_inject_pending_timer_irqs(vcpu);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 9750bb3c5a75..958e00371516 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -38,6 +38,7 @@
 #define KVM_REQ_MIGRATE_TIMER      1
 #define KVM_REQ_REPORT_TPR_ACCESS  2
 #define KVM_REQ_MMU_RELOAD         3
+#define KVM_REQ_TRIPLE_FAULT       4
 
 struct kvm_vcpu;
 extern struct kmem_cache *kvm_vcpu_cache;