From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andrew Cooper <andrew.cooper3@citrix.com>
Subject: Re: [PATCH v3] nested SVM: adjust guest handling of
	structure mappings
Date: Mon, 11 Nov 2013 14:40:43 +0000
Message-ID: <5280EC6B.4080108@citrix.com>
References: <5280A4640200007800101A29@nat28.tlf.novell.com>
	<5280C8830200007800101BCD@nat28.tlf.novell.com>
	<5280BE9E.1060209@citrix.com>
	<5280E13E0200007800101D43@nat28.tlf.novell.com>
	<5280D8A9.5060107@citrix.com>
	<5280EB290200007800101E07@nat28.tlf.novell.com>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <xen-devel-bounces@lists.xen.org>
Received: from mail6.bemta3.messagelabs.com ([195.245.230.39])
	by lists.xen.org with esmtp (Exim 4.72)
	(envelope-from <Andrew.Cooper3@citrix.com>) id 1VfsfX-0007KM-9U
	for xen-devel@lists.xenproject.org; Mon, 11 Nov 2013 14:40:47 +0000
In-Reply-To: <5280EB290200007800101E07@nat28.tlf.novell.com>
List-Unsubscribe: <http://lists.xen.org/cgi-bin/mailman/options/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=unsubscribe>
List-Post: <mailto:xen-devel@lists.xen.org>
List-Help: <mailto:xen-devel-request@lists.xen.org?subject=help>
List-Subscribe: <http://lists.xen.org/cgi-bin/mailman/listinfo/xen-devel>,
	<mailto:xen-devel-request@lists.xen.org?subject=subscribe>
Sender: xen-devel-bounces@lists.xen.org
Errors-To: xen-devel-bounces@lists.xen.org
To: Jan Beulich <JBeulich@suse.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Christoph Egger <chegger@amazon.de>, suravee.suthikulpanit@amd.com
List-Id: xen-devel@lists.xenproject.org

On 11/11/13 13:35, Jan Beulich wrote:
>>>> On 11.11.13 at 14:16, Andrew Cooper <andrew.cooper3@citrix.com> wrote:
>> On 11/11/13 12:53, Jan Beulich wrote:
>>> +    for ( io_bitmap = hvm_map_guest_frame_ro(gfn, 0); ; )
>>> +    {
>>> +        enabled = io_bitmap && test_bit(port, io_bitmap);
>>> +        if ( !enabled || !--size )
>>> +            break;
>>> +        if ( unlikely(++port == 8 * PAGE_SIZE) )
>>> +        {
>>> +            hvm_unmap_guest_frame(io_bitmap, 0);
>>> +            io_bitmap = hvm_map_guest_frame_ro(++gfn, 0);
>>> +            port -= 8 * PAGE_SIZE;
>>> +        }
>>>      }
>> Ok - this safe now, but I don't understand the reasoning for introducing
>> this loop?
>>
>> The ioio exit value gives us a single port, and the size of access on
>> that specific port.
>>
>> The switch statement tells us exactly which gfn the relevant bit refers
>> to, surely a single hvm_map_guest_frame_ro() is sufficient?
> When the operation spans multiple ports (INW, INL, etc), multiple
> bits need to be looked at. And when the access is misaligned and
> crosses a 32k (port number) boundary, more than one page needs
> looking at.
>
> Jan
>

Ah of course.

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>