On Sun, Mar 21, 2010 at 04:41:24PM +0200, Avi Kivity wrote:
> On 03/21/2010 01:08 PM, Gleb Natapov wrote:
> >Decode CMPXCHG8B destination operand in decoding stage. Fixes regression
> >introduced by "If LOCK prefix is used dest arg should be memory" commit.
> >This commit relies on dst operand be decoded at the beginning of an
> >instruction emulation.
>
> >@@ -1719,15 +1719,12 @@ static inline int emulate_grp9(struct
> >x86_emulate_ctxt *ctxt,
> > c->regs[VCPU_REGS_RAX] = (u32) (old>> 0);
> > c->regs[VCPU_REGS_RDX] = (u32) (old>> 32);
> > ctxt->eflags&= ~EFLG_ZF;
> >-
> > } else {
> >- new = ((u64)c->regs[VCPU_REGS_RCX]<< 32) |
> >+ c->dst.val = ((u64)c->regs[VCPU_REGS_RCX]<< 32) |
> > (u32) c->regs[VCPU_REGS_RBX];
> >
> >- rc = ops->cmpxchg_emulated(c->modrm_ea,&old,&new, 8,
> >ctxt->vcpu);
> >- if (rc != X86EMUL_CONTINUE)
> >- return rc;
> > ctxt->eflags |= EFLG_ZF;
> >+ c->lock_prefix = 1;
>
> Why is this bit needed? cmpxchg64b without lock is valid and racy,
> but the guest may know it is safe.
>
Agree. Before this patch cmpxchg8b emulation always called
cmpxchg_emulated(), so to be extra careful I wanted to preserve old
behaviour. Resend the patch without this line?
--
Gleb.
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