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

["Christoph Egger" <Christoph.Egger@xxxxxxx>]

On Saturday 12 January 2008 12:10:58 Keir Fraser wrote:
> Fixed by c/s 16709. I tested with the ISO you sent me and NetBSD boots much
> further,

I can confirm that. I tested with c/s 16712. Thanks for fixing this.

> to a reasonable point (failure to init a console). 

It launches  "sysinst", the install application. Press CTRL+Z get back
on console.

Christoph


>
>  -- 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>



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