KVM: Drop interrupt shadow when single stepping should be done only on VMX

The problem exists only on VMX. Also currently we skip this step if
there is pending exception. The patch fixes this too.

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

1 files changed, 8 insertions, 0 deletions

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index c87c93fd129a..c14bffc8c1f9 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3453,6 +3453,14 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu, struct kvm_run *kvm_run)
         if (test_bit(VCPU_REGS_RIP, (unsigned long *)&vcpu->arch.regs_dirty))
                 vmcs_writel(GUEST_RIP, vcpu->arch.regs[VCPU_REGS_RIP]);
 
+        /* 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. */
+        if (vcpu->guest_debug & KVM_GUESTDBG_SINGLESTEP)
+                vmx_set_interrupt_shadow(vcpu, 0);
+
         /*
          * Loading guest fpu may have cleared host cr0.ts
          */