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Re: [Xen-devel] [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE
- To: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>, Jason Andryuk <jandryuk@xxxxxxxxx>, Paul Durrant <Paul.Durrant@xxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Thu, 14 Mar 2019 19:37:21 +0000
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- Cc: Anthony Perard <anthony.perard@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, "qemu-devel@xxxxxxxxxx" <qemu-devel@xxxxxxxxxx>, "marmarek@xxxxxxxxxxxxxxxxxxxxxx" <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Thu, 14 Mar 2019 19:37:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Openpgp: preference=signencrypt
On 14/03/2019 19:22, Simon Gaiser wrote:
> Jason Andryuk:
>> On Wed, Mar 13, 2019 at 11:09 AM Paul Durrant <Paul.Durrant@xxxxxxxxxx>
>> wrote:
>>>> -----Original Message-----
>>>> From: Jason Andryuk [mailto:jandryuk@xxxxxxxxx]
>>>> Sent: 11 March 2019 18:02
>>>> To: qemu-devel@xxxxxxxxxx
>>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; marmarek@xxxxxxxxxxxxxxxxxxxxxx; Simon
>>>> Gaiser
>>>> <simon@xxxxxxxxxxxxxxxxxxxxxx>; Jason Andryuk <jandryuk@xxxxxxxxx>;
>>>> Stefano Stabellini
>>>> <sstabellini@xxxxxxxxxx>; Anthony Perard <anthony.perard@xxxxxxxxxx>; Paul
>>>> Durrant
>>>> <Paul.Durrant@xxxxxxxxxx>
>>>> Subject: [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE
>>>>
>>>> From: Simon Gaiser <simon@xxxxxxxxxxxxxxxxxxxxxx>
>>>>
>>>> If a pci memory region has a size < XEN_PAGE_SIZE it can get located at
>>>> an address which is not page aligned.
>>> IIRC the PCI spec says that the minimum memory region size should be at
>>> least 4k. Should we even be tolerating BARs smaller than that?
>>>
>>> Paul
>>>
>> Hi, Paul.
>>
>> Simon found this, so it affects a real device. Simon, do you recall
>> which device was affected?
> Not sure which one it was. Probably the USB controller or the SD host
> controller. As your example below shows this is not so uncommon.
The minimum is 128 bytes, not 4k - I've just checked the PCIe spec.
Xen/Qemu definitely needs to cope with smaller than 4k if we want to be
spec compliant.
~Andrew
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