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, 4 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index adcf73871a9d..bb04f11bf70f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3935,7 +3935,10 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
                 kvm_x86_ops->set_rflags(vcpu, eflags & ~X86_EFLAGS_NT);
         }
 
-        kvm_x86_ops->skip_emulated_instruction(vcpu);
+        /* set back link to prev task only if NT bit is set in eflags
+           note that old_tss_sel is not used afetr this point */
+        if (reason != TASK_SWITCH_CALL && reason != TASK_SWITCH_GATE)
+                old_tss_sel = 0xffff;
 
         /* set back link to prev task only if NT bit is set in eflags
            note that old_tss_sel is not used afetr this point */