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Re: [Xen-devel] [PATCH][HVM] Fix guest hang producing "PIT: bad access"messages
- To: Christoph Egger <Christoph.Egger@xxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
- From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
- Date: Sat, 12 Jan 2008 11:10:58 +0000
- Delivery-date: Sat, 12 Jan 2008 03:11:21 -0800
- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
- Thread-index: AchVC86lDTA2b8D/EdyMtwAWy6hiGQ==
- Thread-topic: [Xen-devel] [PATCH][HVM] Fix guest hang producing "PIT: bad access"messages
Fixed by c/s 16709. I tested with the ISO you sent me and NetBSD boots much
further, to a reasonable point (failure to init a console).
On 11/1/08 11:08, "Christoph Egger" <Christoph.Egger@xxxxxxx> wrote:
> 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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