Re: [virtio-comment] [PATCH v3 0/1] virtio-pmem: Support describing pmem as shared memory region

[Cornelia Huck <cohuck@redhat.com>]

On Wed, Jul 28 2021, tstark@linux.microsoft.com wrote:

> From: Taylor Stark <tstark@microsoft.com>
>
> Changes from v2 [1]:
>  - Incorporated suggestions from Cornelia Huck on rewording driver initialization.
>
> Changes from v1:
>  - Added in a feature bit (VIRTIO_PMEM_F_SHMEM_REGION) for controlling how the
>    device indicates the guest physical address ranges to the driver. This feature
>    directly affects control flow of the driver, since it seemed weird to have
>    the driver indicate support for shared memory regions, and then needing
>    to include an enum (or similar) informing the driver how the device
>    indicated guest physical address ranges. If devices want to indicate the
>    ranges as guest absolute addresses, they can skip negotiating the feature.
>  - The linux driver implementation has been updated and tested, but I'm holding
>    off on posting the patches to get some feedback on the new approach.
>  - Moved some changes to proper subsections (normative subsections).
>
> [1] https://lists.oasis-open.org/archives/virtio-comment/202107/msg00145.html
>
> ---
>
> This patch updates the virtio-pmem spec to add support for describing the pmem
> region as a shared memory region. This is required to support virtio-pmem in
> Hyper-V, since Hyper-V only allows PCI devices to operate on memory ranges
> defined via BARs. When using the virtio PCI transport, shared memory regions
> are described via PCI BARs.
>
> As virtio-pmem hasn't been added to the virtio spec yet (see this issue [1]),
> this patch is based off the RFC spec [2]. The linux driver implementation has
> been posted at [3].
>
> [1] https://github.com/oasis-tcs/virtio-spec/issues/78
> [2] https://lists.oasis-open.org/archives/virtio-dev/201903/msg00083.html
> [3] https://lore.kernel.org/nvdimm/20210715223505.GA29329@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net
>
> Taylor Stark (1):
>   virtio-pmem: Support describing pmem as shared memory region
>
>  conformance.tex |  1 +
>  virtio-pmem.tex | 34 +++++++++++++++++++++++++++++-----
>  2 files changed, 30 insertions(+), 5 deletions(-)
>

Looks good to me now, but I'd also like a comment from someone who has
actually done some work in the area.

The main issue is to get the actual (base) pmem spec merged, but I see
that a patch has been posted, so we should be able to go from there.