Re: [PATCH] vfio-pci: Allow to mmap sub-page MMIO BARs if the mmio page is exclusive

[Yongji Xie <xyjxie@linux.vnet.ibm.com>]

On 2016/5/3 14:11, Tian, Kevin wrote:

>> From: Yongji Xie [mailto:xyjxie@linux.vnet.ibm.com]
>> Sent: Tuesday, May 03, 2016 1:52 PM
>>
>>>> +
>>>> +		if (!(res->start & ~PAGE_MASK)) {
>>>> +			/*
>>>> +			 * Add shadow resource for sub-page bar whose mmio
>>>> +			 * page is exclusive in case that hot-add device's
>>>> +			 * bar is assigned into the mem hole.
>>>> +			 */
>>>> +			shadow_res = kzalloc(sizeof(*shadow_res), GFP_KERNEL);
>>>> +			shadow_res->resource.start = res->end + 1;
>>>> +			shadow_res->resource.end = res->start + PAGE_SIZE - 1;
>>> What about res->start not page aligned so you end up still having
>>> a portion before res->start not exclusively reserved?
>> Do you mean add a 'dummy' resource to reserve the portion
>> before res->start if res->start not page aligned?
>>
>> But would it happen that there is a mem hole in the portion
>> before res->start? The resource should have been assigned
>> into the hole at the beginning.
>>
> Just a quick thought. Another device might occupy that range
> before initializing this device, and then 'another device' is hot
> removed later...
>
> Thanks
> Kevin

That's a good point! I will add support for this case in v2.

Thanks,
Yongji