KVM: Fix unneeded instruction skipping during task switching.

There is no need to skip instruction if the reason for a task switch
is a task gate in IDT and access to it is caused by an external even.
The problem  is currently solved only for VMX since there is no reliable
way to skip an instruction in SVM. We should emulate it instead.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 18 insertions, 7 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index de741043c5b1..bba67b70c4b0 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1825,17 +1825,28 @@ static int task_switch_interception(struct vcpu_svm *svm,
                                     struct kvm_run *kvm_run)
 {
         u16 tss_selector;
+        int reason;
+        int int_type = svm->vmcb->control.exit_int_info &
+                SVM_EXITINTINFO_TYPE_MASK;
 
         tss_selector = (u16)svm->vmcb->control.exit_info_1;
+
         if (svm->vmcb->control.exit_info_2 &
             (1ULL << SVM_EXITINFOSHIFT_TS_REASON_IRET))
-                return kvm_task_switch(&svm->vcpu, tss_selector,
-                                       TASK_SWITCH_IRET);
-        if (svm->vmcb->control.exit_info_2 &
-            (1ULL << SVM_EXITINFOSHIFT_TS_REASON_JMP))
-                return kvm_task_switch(&svm->vcpu, tss_selector,
-                                       TASK_SWITCH_JMP);
-        return kvm_task_switch(&svm->vcpu, tss_selector, TASK_SWITCH_CALL);
+                reason = TASK_SWITCH_IRET;
+        else if (svm->vmcb->control.exit_info_2 &
+                 (1ULL << SVM_EXITINFOSHIFT_TS_REASON_JMP))
+                reason = TASK_SWITCH_JMP;
+        else if (svm->vmcb->control.exit_int_info & SVM_EXITINTINFO_VALID)
+                reason = TASK_SWITCH_GATE;
+        else
+                reason = TASK_SWITCH_CALL;
+
+
+        if (reason != TASK_SWITCH_GATE || int_type == SVM_EXITINTINFO_TYPE_SOFT)
+                skip_emulated_instruction(&svm->vcpu);
+
+        return kvm_task_switch(&svm->vcpu, tss_selector, reason);
 }
 
 static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)