KVM: VMX: Allow single-stepping when uninterruptible

When single-stepping over STI and MOV SS, we must clear the
corresponding interruptibility bits in the guest state. Otherwise
vmentry fails as it then expects bit 14 (BS) in pending debug exceptions
being set, but that's not correct for the guest debugging case.

Note that clearing those bits is safe as we check for interruptibility
based on the original state and do not inject interrupts or NMIs if
guest interruptibility was blocked.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 7d2d6ff74fa1bf6516396904f0112e97e91107ae..e16d4a62464fdd98c38935191f3d70e4172b3a40 100644 (file)
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2477,6 +2477,11 @@ static void do_interrupt_requests(struct kvm_vcpu *vcpu,
 {
        vmx_update_window_states(vcpu);
 
+       if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+               vmcs_clear_bits(GUEST_INTERRUPTIBILITY_INFO,
+                               GUEST_INTR_STATE_STI |
+                               GUEST_INTR_STATE_MOV_SS);
+
        if (vcpu->arch.nmi_pending && !vcpu->arch.nmi_injected) {
                if (vcpu->arch.interrupt.pending) {
                        enable_nmi_window(vcpu);
@@ -3243,6 +3248,11 @@ static void vmx_intr_assist(struct kvm_vcpu *vcpu)
 
        vmx_update_window_states(vcpu);
 
+       if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+               vmcs_clear_bits(GUEST_INTERRUPTIBILITY_INFO,
+                               GUEST_INTR_STATE_STI |
+                               GUEST_INTR_STATE_MOV_SS);
+
        if (vcpu->arch.nmi_pending && !vcpu->arch.nmi_injected) {
                if (vcpu->arch.interrupt.pending) {
                        enable_nmi_window(vcpu);