KVM: x86: add comments where MMIO does not return to the emulator

Support for single-step in the emulator (new in 3.12) does not work for
MMIO or PIO writes, because they are completed without returning to
the emulator.  This is not worse than what we had in 3.11; still, add
comments so that the issue is not forgotten.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

1 files changed, 5 insertions, 2 deletions

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index cb276e976203..e514b3cb8b93 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5122,9 +5122,10 @@ restart:
                 inject_emulated_exception(vcpu);
                 r = EMULATE_DONE;
         } else if (vcpu->arch.pio.count) {
-                if (!vcpu->arch.pio.in)
+                if (!vcpu->arch.pio.in) {
+                        /* FIXME: return into emulator if single-stepping.  */
                         vcpu->arch.pio.count = 0;
-                else {
+                } else {
                         writeback = false;
                         vcpu->arch.complete_userspace_io = complete_emulated_pio;
                 }
@@ -6176,6 +6177,8 @@ static int complete_emulated_mmio(struct kvm_vcpu *vcpu)
 
         if (vcpu->mmio_cur_fragment == vcpu->mmio_nr_fragments) {
                 vcpu->mmio_needed = 0;
+
+                /* FIXME: return into emulator if single-stepping.  */
                 if (vcpu->mmio_is_write)
                         return 1;
                 vcpu->mmio_read_completed = 1;