WARNING - OLD ARCHIVES

This is an archived copy of the Xen.org mailing list, which we have preserved to ensure that existing links to archives are not broken. The live archive, which contains the latest emails, can be found at http://lists.xen.org/
   
 
 
Xen 
 
Home Products Support Community News
 
   
 

xen-devel

Re: [Xen-devel] [PATCH][HVM] Fix guest hang producing "PIT: bad access"m

To: Christoph Egger <Christoph.Egger@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH][HVM] Fix guest hang producing "PIT: bad access"messages
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 11 Jan 2008 11:52:45 +0000
Delivery-date: Fri, 11 Jan 2008 03:53:29 -0800
Envelope-to: www-data@xxxxxxxxxxxxxxxxxx
In-reply-to: <200801111208.02078.Christoph.Egger@xxxxxxx>
List-help: <mailto:xen-devel-request@lists.xensource.com?subject=help>
List-id: Xen developer discussion <xen-devel.lists.xensource.com>
List-post: <mailto:xen-devel@lists.xensource.com>
List-subscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=subscribe>
List-unsubscribe: <http://lists.xensource.com/cgi-bin/mailman/listinfo/xen-devel>, <mailto:xen-devel-request@lists.xensource.com?subject=unsubscribe>
Sender: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
Thread-index: AchUSHqFuVoA+MA7EdymsQAX8io7RQ==
Thread-topic: [Xen-devel] [PATCH][HVM] Fix guest hang producing "PIT: bad access"messages
User-agent: Microsoft-Entourage/11.3.6.070618
Okay, but the patch is buggy (accesses count*size bytes of memory, but
actually only one byte-sized port will be accessed) and actually this is
indicative of a wider issue in other Xen-emulated devices. We need a more
cooked interface to PIO handlers. I'll take a look.

 -- Keir

On 11/1/08 11:08, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:

> 
> Hi
> 
> When the HVM guest atomically reads two bytes from the PIT via  "rep insb"
> and the two bytes crosses pages, then in xen/arch/x86/hvm/i8254.c,
> handle_pit_io(), p->data_is_ptr is 1 which leads to an unhandled read.
> 
> Since reading the first byte does not change the guest rip, an endless loop
> of VMEXIT_IOIO happens. This leads to an endless stream of "PIT: bad access"
> xen messages => Guest hangs.
> 
> This has been accurately reproduced on NetBSD/amd64 as HVM guest
> and this also been seen on 64bit Windows guests.
> 
> The attached patch handles the page-crossing access in the PIT emulation.
> 
> Signed-off-by: Christoph Egger <Christoph.Egger@xxxxxxx>
> 



_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel