[PATCH 1/2] KVM: x86: Setting rflags.rf during rep-string emulation

[Nadav Amit]

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@xxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 8d41556..57743ed 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;
-- 
1.9.1

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