From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [PATCH] x86 emulator: Add IRET instruction
Date: Wed, 28 Jul 2010 15:30:10 +0200
Message-ID: <4C5030E2.8050202@redhat.com>
References: <1280309920-13539-1-git-send-email-m.gamal005@gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: avi@redhat.com, mtosatti@redhat.com, kvm@vger.kernel.org
To: Mohammed Gamal <m.gamal005@gmail.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mail-qy0-f174.google.com ([209.85.216.174]:56345 "EHLO
	mail-qy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751158Ab0G1NaY (ORCPT <rfc822;kvm@vger.kernel.org>);
	Wed, 28 Jul 2010 09:30:24 -0400
Received: by qyk7 with SMTP id 7so3535627qyk.19
        for <kvm@vger.kernel.org>; Wed, 28 Jul 2010 06:30:23 -0700 (PDT)
In-Reply-To: <1280309920-13539-1-git-send-email-m.gamal005@gmail.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

On 07/28/2010 11:38 AM, Mohammed Gamal wrote:
> +	unsigned long mask = EFLG_CF | EFLG_PF | EFLG_AF | EFLG_ZF | EFLG_SF | EFLG_TF |
> +			     EFLG_IF | EFLG_DF | EFLG_OF | EFLG_IOPL | EFLG_NT | EFLG_RF |
> +			     EFLG_AC | EFLG_ID | (1 << 1); /* Last one is the reserved bit */
> +	unsigned long vm86_mask = EFLG_VM | EFLG_VIF | EFLG_VIP;
> ...
> +	if (c->op_bytes == 4)
> +		ctxt->eflags = ((temp_eflags & mask) | (ctxt->eflags & vm86_mask));
> +	else if (c->op_bytes == 2) {
> +		ctxt->eflags &= ~0xffff;
> +		ctxt->eflags |= temp_eflags;
> +	}

I think that's still not it.  You can set reserved bits for c->op_bytes 
== 2, and you can clear bit 1 for both 16- and 32-bit IRET.

IOW you need something like this:

     mask = ...; /* without (1 << 1); */
     ctxt_mask = (1 << 1) | EFLG_VM | EFLG_VIF | EFLG_VIP;

     if (c->op_bytes == 2) {
         mask &= 0xffff;
         ctxt_mask |= ~0xffff;
     }

     ctxt->eflags = (temp_eflags & mask) | (ctxt->eflags & ctxt_mask);

Paolo