KVM: x86: hardware task switching support

This emulates the x86 hardware task switch mechanism in software, as it is
unsupported by either vmx or svm.  It allows operating systems which use it,
like freedos, to run as kvm guests.

Signed-off-by: Izik Eidus <izike@qumranet.com>
Signed-off-by: Avi Kivity <avi@qumranet.com>

1 files changed, 12 insertions, 3 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index c1c1b973e80a..ad273468c08a 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1112,9 +1112,18 @@ static int invalid_op_interception(struct vcpu_svm *svm,
 static int task_switch_interception(struct vcpu_svm *svm,
                                     struct kvm_run *kvm_run)
 {
-        pr_unimpl(&svm->vcpu, "%s: task switch is unsupported\n", __func__);
-        kvm_run->exit_reason = KVM_EXIT_UNKNOWN;
-        return 0;
+        u16 tss_selector;
+
+        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);
 }
 
 static int cpuid_interception(struct vcpu_svm *svm, struct kvm_run *kvm_run)