From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH 3/7] KVM: x86 emulator: introduce NoWrite flag
Date: Sat, 22 Dec 2012 18:20:49 +0200
Message-ID: <20121222162049.GY29007@redhat.com>
References: <1356179217-5526-1-git-send-email-avi.kivity@gmail.com>
 <1356179217-5526-4-git-send-email-avi.kivity@gmail.com>
 <20121222151111.GW29007@redhat.com>
 <CAEbWaipz3z=UOV7cNrnbd4PzFhZ6WWcKN-V8t7DP+Wxt9pFpKw@mail.gmail.com>
 <20121222153934.GX29007@redhat.com>
 <CAEbWaip2iidnPYnxqaYmBfkgji98XBjLemsfwyLFYr=vjwh-VA@mail.gmail.com>
 <CAEbWaiqu4Fe-U+VwAji0hFd4GUAUd=3f2g7vd1ENYrdawKxg8A@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Marcelo Tosatti <mtosatti@redhat.com>, kvm <kvm@vger.kernel.org>
To: Avi Kivity <avi.kivity@gmail.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:22280 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751651Ab2LVQUw (ORCPT <rfc822;kvm@vger.kernel.org>);
	Sat, 22 Dec 2012 11:20:52 -0500
Content-Disposition: inline
In-Reply-To: <CAEbWaiqu4Fe-U+VwAji0hFd4GUAUd=3f2g7vd1ENYrdawKxg8A@mail.gmail.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Sat, Dec 22, 2012 at 05:51:08PM +0200, Avi Kivity wrote:
> On Sat, Dec 22, 2012 at 5:45 PM, Avi Kivity <avi.kivity@gmail.com> wrote:
> > On Sat, Dec 22, 2012 at 5:39 PM, Gleb Natapov <gleb@redhat.com> wrote:
> >> On Sat, Dec 22, 2012 at 05:28:00PM +0200, Avi Kivity wrote:
> >>> On Sat, Dec 22, 2012 at 5:11 PM, Gleb Natapov <gleb@redhat.com> wrote:
> >>> >>  #define X2(x...) x, x
> >>> >>  #define X3(x...) X2(x), x
> >>> >> @@ -1584,6 +1585,9 @@ static int writeback(struct x86_emulate_ctxt *ctxt)
> >>> >>  {
> >>> >>       int rc;
> >>> >>
> >>> >> +     if (ctxt->d & NoWrite)
> >>> >> +             return X86EMUL_CONTINUE;
> >>> >> +
> >>> > Why not make it Dst flag and set dst.type to OP_NONE during decoding
> >>> > instead of this special case?
> >>>
> >>> My thinking was to eventually convert everything to NoWrite, then it's
> >>> not a special case.  But your approach works too, I can change it if
> >>> you like.  We'll have an if () either way though.
> >> But meanwhile we will have two different ways to disable writeback. When
> >> all instructions will be marked with NoWrite we can switch it easily if
> >> we want. Also some instruction can disable writeback conditionally. cmov is one
> >> (and may be only) of them.
> >
> > Makes sense, will update for the next iteration.
> 
> Actually that doesn't work. x86_emulate_insn() needs dst.type in order
> to fetch the operand.
True :(. Actually if we will move from OP_NONE to NoWrite we can drop
saved_dst_type hack from x86_emulate_insn.

--
			Gleb.