KVM: x86: Setting rflags.rf during rep-string emulation

This patch updates RF for rep-string emulation.  The flag is set upon the first
iteration, and cleared after the last (if emulated). It is intended to make
sure that if a trap (in future data/io #DB emulation) or interrupt is delivered
to the guest during the rep-string instruction, RF will be set correctly. RF
affects whether instruction breakpoint in the guest is masked.

Signed-off-by: Nadav Amit <namit@cs.technion.ac.il>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8d415563e05b..57743edfb4e2 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -4683,7 +4683,10 @@ special_insn:
                         goto done;
         }
 
-        ctxt->eflags &= ~EFLG_RF;
+        if (ctxt->rep_prefix && (ctxt->d & String))
+                ctxt->eflags |= EFLG_RF;
+        else
+                ctxt->eflags &= ~EFLG_RF;
 
         if (ctxt->execute) {
                 if (ctxt->d & Fastop) {
@@ -4824,6 +4827,7 @@ writeback:
                         }
                         goto done; /* skip rip writeback */
                 }
+                ctxt->eflags &= ~EFLG_RF;
         }
 
         ctxt->eip = ctxt->_eip;