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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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