Re: [Qemu-devel] [PATCH v2] vfio: Add support for mmapping sub-page MMIO BARs

[Yongji Xie]

On 2016/10/1 0:05, Paolo Bonzini wrote:

> On 14/09/2016 00:55, Alex Williamson wrote:
> > Paolo, as the reigning memory API expert, do you see any issues with
> > this?  Expanding the size of a container MemoryRegion and the contained
> > mmap'd subregion and manipulating priorities so that we don't interfere
> > with other MemoryRegions.
> I guess it's fine if you are okay with maintaining it.
> memory_region_set_size exists, might as well use it. :)
>
> What I'm worried about, is what happens if two such regions end up in
> the same guest page.  Then the two priorities conflict.

Hi Paolo,

I think I can answer this question. We would expand only one MemoryRegion
which is page aligned and set its priority to zero if we have two region 
in the same
guest page. Then the Memory Region with higher priority will overlap the 
expanded
part of page aligned one as if we didn't do the expanding.

Thanks,
Yongji