Re: [PATCH 4/4] KVM: x86 emulator: fix REPZ/REPNZ termination condition

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 On 08/17/2010 12:13 PM, Gleb Natapov wrote:
On Tue, Aug 17, 2010 at 11:26:43AM +0300, Avi Kivity wrote:
EFLAGS.ZF needs to be checked after each iteration, not before.

Signed-off-by: Avi Kivity<avi@xxxxxxxxxx>
---
  arch/x86/kvm/emulate.c |   42 +++++++++++++++++++++++-------------------
  1 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 0c0ada9..a2edfb1 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2747,6 +2747,7 @@ x86_emulate_insn(struct x86_emulate_ctxt *ctxt)
  	int rc = X86EMUL_CONTINUE;
  	int saved_dst_type = c->dst.type;
  	int irq; /* Used for int 3, int, and into */
+	ulong old_eip;
Is never used.


Whoops.

@@ -3250,13 +3234,33 @@ writeback:
  	if (c->rep_prefix&&  (c->d&  String)) {
  		struct read_cache *rc =&ctxt->decode.io_read;
  		register_address_increment(c,&c->regs[VCPU_REGS_RCX], -1);
+		/* The second termination condition only applies for REPE
+		 * and REPNE. Test if the repeat string operation prefix is
+		 * REPE/REPZ or REPNE/REPNZ and if it's the case it tests the
+		 * corresponding termination condition according to:
+		 * 	- if REPE/REPZ and ZF = 0 then done
+		 * 	- if REPNE/REPNZ and ZF = 1 then done
+		 */
+		if ((c->b == 0xa6) || (c->b == 0xa7) ||
+		    (c->b == 0xae) || (c->b == 0xaf)) {
+			trace_printk("c->eip %lx ctxt->eip %lx\n",
+				     c->eip, ctxt->eip);
+			if (((c->rep_prefix == REPE_PREFIX)&&
+			     ((ctxt->eflags&  EFLG_ZF) == 0))
+			    || ((c->rep_prefix == REPNE_PREFIX)&&
+				((ctxt->eflags&  EFLG_ZF) == EFLG_ZF))) {
+				ctxt->restart = false;
Why not jump to string_done label here?

It does a 'goto done;' which skips a couple of things.

+			}
+		}
  		/*
  		 * Re-enter guest when pio read ahead buffer is empty or,
  		 * if it is not used, after each 1024 iteration.
  		 */
  		if ((rc->end == 0&&  !(c->regs[VCPU_REGS_RCX]&  0x3ff)) ||
-		    (rc->end != 0&&  rc->end == rc->pos))
+		    (rc->end != 0&&  rc->end == rc->pos)) {
  			ctxt->restart = false;
+			c->eip = ctxt->eip;
We can get here when instruction is completed by above "if", so same
instruction will reexecute once again.

Not good.  Will redo (and write tests).


--
error compiling committee.c: too many arguments to function

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