| Message ID | 20110329013229.20e6168f.takuya.yoshikawa@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 03/28/2011 06:32 PM, Takuya Yoshikawa wrote: > From: Takuya Yoshikawa<yoshikawa.takuya@oss.ntt.co.jp> > > This stops "CMP r/m, reg" to write back the data into memory. > Pointed out by Avi. > > Signed-off-by: Takuya Yoshikawa<yoshikawa.takuya@oss.ntt.co.jp> > --- > arch/x86/kvm/emulate.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c > index 14c5ad5..8a73805 100644 > --- a/arch/x86/kvm/emulate.c > +++ b/arch/x86/kvm/emulate.c > @@ -3084,6 +3084,7 @@ special_insn: > emulate_2op_SrcV("xor", c->src, c->dst, ctxt->eflags); > break; > case 0x38 ... 0x3d: > + c->dst.type = OP_NONE; /* Disable writeback. */ > cmp: /* cmp */ Why not disable writeback here? As a prelude to having em_cmp() which does everything? I see SCAS also does a 'goto cmp', but it also benefits from disabling writeback. > emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags); > break; > @@ -3138,6 +3139,7 @@ special_insn: > case 6: > goto xor; > case 7: > + c->dst.type = OP_NONE; /* Disable writeback. */ > goto cmp; > } > break;
diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c index 14c5ad5..8a73805 100644 --- a/arch/x86/kvm/emulate.c +++ b/arch/x86/kvm/emulate.c @@ -3084,6 +3084,7 @@ special_insn: emulate_2op_SrcV("xor", c->src, c->dst, ctxt->eflags); break; case 0x38 ... 0x3d: + c->dst.type = OP_NONE; /* Disable writeback. */ cmp: /* cmp */ emulate_2op_SrcV("cmp", c->src, c->dst, ctxt->eflags); break; @@ -3138,6 +3139,7 @@ special_insn: case 6: goto xor; case 7: + c->dst.type = OP_NONE; /* Disable writeback. */ goto cmp; } break;