On Tue, Aug 24, 2010 at 04:11:20PM +0300, Avi Kivity wrote:
> On 08/24/2010 02:30 PM, Gleb Natapov wrote:
> >Signed-off-by: Gleb Natapov<gleb@xxxxxxxxxx>
> >---
> > arch/x86/kvm/emulate.c | 42 +++++++++++++++++++++++++++++-------------
> > 1 files changed, 29 insertions(+), 13 deletions(-)
> >
> >diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
> >index f9f8353..d34d706 100644
> >--- a/arch/x86/kvm/emulate.c
> >+++ b/arch/x86/kvm/emulate.c
> >@@ -2921,6 +2921,32 @@ done:
> > return (rc == X86EMUL_UNHANDLEABLE) ? -1 : 0;
> > }
> >
> >+static bool string_inst_completed(struct x86_emulate_ctxt *ctxt)
>
> s/inst/insn/.
>
> >+{
> >+ struct decode_cache *c =&ctxt->decode;
> >+
> >+ /* All REP prefixes have the same first termination condition */
> >+ if (address_mask(c, c->regs[VCPU_REGS_RCX]) == 0)
> >+ return true;
>
> This is checked during the beginning of the instruction, not after
> completion. Why is it here? it will just be duplicated.
>
SDM describes REP instruction algorithm this way:
WHILE CountReg ≠ 0
DO
Service pending interrupts (if any);
Execute associated string instruction;
CountReg ← (CountReg – 1);
IF CountReg = 0
THEN exit WHILE loop; FI;
IF (Repeat prefix is REPZ or REPE) and (ZF = 0)
or (Repeat prefix is REPNZ or REPNE) and (ZF = 1)
THEN exit WHILE loop; FI;
OD;
So CountReg is checked at the beginning and after each iteration.
Practically it will save us one return to a guest and exit back
to emulator at the end of rep instruction (not a big deal).
> >+
> >+ /* 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))
> >+ && (((c->rep_prefix == REPE_PREFIX)&&
> >+ ((ctxt->eflags& EFLG_ZF) == 0))
> >+ || ((c->rep_prefix == REPNE_PREFIX)&&
> >+ ((ctxt->eflags& EFLG_ZF) == EFLG_ZF))))
> >+ return true;
> >+
> >+ return false;
> >+}
> >+
>
> --
> error compiling committee.c: too many arguments to function
--
Gleb.
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