From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: [PATCH 2/2] Provide fast path for "rep ins" emulation if
 possible.
Date: Tue, 5 Jun 2012 20:19:19 +0300
Message-ID: <20120605171919.GH20236@redhat.com>
References: <1337782095-32287-1-git-send-email-gleb@redhat.com>
 <1337782095-32287-3-git-send-email-gleb@redhat.com>
 <4FCE2ECB.8080103@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: kvm@vger.kernel.org, mtosatti@redhat.com
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:57385 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1755023Ab2FERTU (ORCPT <rfc822;kvm@vger.kernel.org>);
	Tue, 5 Jun 2012 13:19:20 -0400
Received: from int-mx09.intmail.prod.int.phx2.redhat.com (int-mx09.intmail.prod.int.phx2.redhat.com [10.5.11.22])
	by mx1.redhat.com (8.14.4/8.14.4) with ESMTP id q55HJKGn012753
	(version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK)
	for <kvm@vger.kernel.org>; Tue, 5 Jun 2012 13:19:20 -0400
Content-Disposition: inline
In-Reply-To: <4FCE2ECB.8080103@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On Tue, Jun 05, 2012 at 07:07:39PM +0300, Avi Kivity wrote:
> > +
> > +	count = (PAGE_SIZE - offset_in_page(linear_addr))/size;
> > +
> > +	if (count == 0) /* 'in' crosses page boundry */
> > +		return EMULATE_FAIL;
> > +
> > +	count = min(count, rcx);
> > +
> > +	r = __kvm_fast_string_pio_in(vcpu, size, port, linear_addr, count);
> > +
> > +	if (r != EMULATE_DO_MMIO)
> > +		return r;
> > +
> > +	vcpu->arch.fast_string_pio_ctxt.linear_addr = linear_addr;
> > +	vcpu->arch.complete_userspace_io = complete_fast_string_pio;
> > +	return EMULATE_DO_MMIO;
> > +}
> > +EXPORT_SYMBOL_GPL(kvm_fast_string_pio_in);
> 
> Perhaps a better way to do it is to move the code into the emulator,
> which already handles all the checks and masks, and just avoid
> x86_decode_insn()/x86_emulate_insn().
> 
I do not see how it would be better. Emulator works on different data
structures that should be prepared and the only functions that we can
reuse (as far as I see) are register_address_increment() and ad_mask()
anyway.

--
			Gleb.