KVM: Deal with interrupt shadow state for emulated instructions

We currently unblock shadow interrupt state when we skip an instruction,
but failing to do so when we actually emulate one. This blocks interrupts
in key instruction blocks, in particular sti; hlt; sequences

If the instruction emulated is an sti, we have to block shadow interrupts.
The same goes for mov ss. pop ss also needs it, but we don't currently
emulate it.

Without this patch, I cannot boot gpxe option roms at vmx machines.
This is described at https://bugzilla.redhat.com/show_bug.cgi?id=494469

Signed-off-by: Glauber Costa <glommer@redhat.com>
CC: H. Peter Anvin <hpa@zytor.com>
CC: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7475b029b2ad..48f744ff0bc1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2379,7 +2379,7 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
                         u16 error_code,
                         int emulation_type)
 {
-        int r;
+        int r, shadow_mask;
         struct decode_cache *c;
 
         kvm_clear_exception_queue(vcpu);
@@ -2433,6 +2433,10 @@ int emulate_instruction(struct kvm_vcpu *vcpu,
         }
 
         r = x86_emulate_insn(&vcpu->arch.emulate_ctxt, &emulate_ops);
+        shadow_mask = vcpu->arch.emulate_ctxt.interruptibility;
+
+        if (r == 0)
+                kvm_x86_ops->set_interrupt_shadow(vcpu, shadow_mask);
 
         if (vcpu->arch.pio.string)
                 return EMULATE_DO_MMIO;