Re: [Qemu-devel] [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE

[Andrew Cooper]

On 14/03/2019 19:22, Simon Gaiser wrote:
> Jason Andryuk:
>> On Wed, Mar 13, 2019 at 11:09 AM Paul Durrant <address@hidden> wrote:
>>>> -----Original Message-----
>>>> From: Jason Andryuk [mailto:address@hidden
>>>> Sent: 11 March 2019 18:02
>>>> To: address@hidden
>>>> Cc: address@hidden; address@hidden; Simon Gaiser
>>>> <address@hidden>; Jason Andryuk <address@hidden>; Stefano Stabellini
>>>> <address@hidden>; Anthony Perard <address@hidden>; Paul Durrant
>>>> <address@hidden>
>>>> Subject: [PATCH 6/6] xen-pt: Round pci regions sizes to XEN_PAGE_SIZE
>>>>
>>>> From: Simon Gaiser <address@hidden>
>>>>
>>>> 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