KVM: prevent spurious exit to userspace during task switch emulation.

If kvm_task_switch() fails code exits to userspace without specifying
exit reason, so the previous exit reason is reused by userspace. Fix
this by specifying exit reason correctly.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 78af52222fd2..ab78eb8ba899 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2266,8 +2266,14 @@ static int task_switch_interception(struct vcpu_svm *svm)
              (int_vec == OF_VECTOR || int_vec == BP_VECTOR)))
                 skip_emulated_instruction(&svm->vcpu);
 
-        return kvm_task_switch(&svm->vcpu, tss_selector, reason,
-                               has_error_code, error_code);
+        if (kvm_task_switch(&svm->vcpu, tss_selector, reason,
+                                has_error_code, error_code) == EMULATE_FAIL) {
+                svm->vcpu.run->exit_reason = KVM_EXIT_INTERNAL_ERROR;
+                svm->vcpu.run->internal.suberror = KVM_INTERNAL_ERROR_EMULATION;
+                svm->vcpu.run->internal.ndata = 0;
+                return 0;
+        }
+        return 1;
 }
 
 static int cpuid_interception(struct vcpu_svm *svm)