On 06/22/23 10:25, David Hildenbrand wrote:
> On 22.06.23 09:27, Vivek Kasireddy wrote:
> 
> There are *probably* more issues on the QEMU side when udmabuf is paired
> with things like MADV_DONTNEED/FALLOC_FL_PUNCH_HOLE used for virtio-balloon,
> virtio-mem, postcopy live migration, ... for example, in the vfio/vdpa case
> we make sure that we disallow most of these, because otherwise there can be
> an accidental "disconnect" between the pages mapped into the VM (guest view)
> and the pages mapped into the IOMMU (device view), for example, after a
> reboot.
> 

Yes, this "disconnect" is still possible.  Attached is a test program I
hacked up based on the udmabuf selftest.  You can see different content
in the memfd pages and udma pages.

FYI- I can verify this new udmabuf code is not accessing struct pages of
hugetlb tail pages, as this test program BUG'ed if hugetlb vmemmap
optimization was enabled in the old udmabuf.
-- 
Mike Kravetz