Re: [PATCH v2 1/2] virtio-pmem: Support PCI BAR-relative addresses

[Taylor Stark <tstark@linux.microsoft.com>]

On Tue, Jul 20, 2021 at 08:51:04AM +0200, Pankaj Gupta wrote:
> > > >
> > > > -       virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > > -                       start, &vpmem->start);
> > > > -       virtio_cread_le(vpmem->vdev, struct virtio_pmem_config,
> > > > -                       size, &vpmem->size);
> > > > +       /* Retrieve the pmem device's address and size. It may have been supplied
> > > > +        * as a PCI BAR-relative shared memory region, or as a guest absolute address.
> > > > +        */
> > > > +       have_shm_region = virtio_get_shm_region(vpmem->vdev, &pmem_region,
> > > > +                                               VIRTIO_PMEM_SHMCAP_ID_PMEM_REGION);
> > >
> > > Current implementation of Virtio pmem device in Qemu does not expose
> > > it as PCI BAR.
> > > So, can't test it. Just curious if device side implementation is also
> > > tested for asynchronous
> > > flush case?
> > >
> > > Thanks,
> > > Pankaj
> >
> > Yes, I tested the async flush case as well. We basically call
> > FlushFileBuffers on the backing file, which is Windows' equivalent of
> > fsync. I also briefly tested with qemu to ensure that still works with
> > the patch.
> 
> Thank you for the confirmation. This sounds really good.
> I am also getting back to pending items for virtio-pmem.
> 
> On a side question: Do you guys have any or plan for Windows guest
> implementation
> for virtio-pmem?

Unfortunately, my team doesn't currently have any plans to add a Windows
virtio-pmem implementation. My team is primarily focused on virtualization
in client environments, which is a little different than server environments.
For our Windows-based scenarios, dynamically sized disks are important. It's
tricky to get that to work with pmem+DAX given that Windows isn't state separated.