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

[Yongji Xie]

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

> > From: Yongji Xie [mailto:xyjxie@xxxxxxxxxxxxxxxxxx]
> > 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