Stefan, I hope you had a great vacation!
Thanks for updating the mirror and your review. Your comments all make sense, and I will address your input when I find time - just a quick ack now since I'm travelling next week and will be on vacation the first half of August, so it might be a while. Thanks, Mattias On Thu, Jul 20, 2023 at 8:41 PM Stefan Hajnoczi <stefa...@redhat.com> wrote: > > On Tue, Jul 04, 2023 at 01:06:24AM -0700, Mattias Nissler wrote: > > This series adds basic support for message-based DMA in qemu's vfio-user > > server. This is useful for cases where the client does not provide file > > descriptors for accessing system memory via memory mappings. My motivating > > use > > case is to hook up device models as PCIe endpoints to a hardware design. > > This > > works by bridging the PCIe transaction layer to vfio-user, and the endpoint > > does not access memory directly, but sends memory requests TLPs to the > > hardware > > design in order to perform DMA. > > > > Note that in addition to the 3 commits included, we also need a > > subprojects/libvfio-user roll to bring in this bugfix: > > https://github.com/nutanix/libvfio-user/commit/bb308a2e8ee9486a4c8b53d8d773f7c8faaeba08 > > Stefan, can I ask you to kindly update the > > https://gitlab.com/qemu-project/libvfio-user mirror? I'll be happy to > > include > > an update to subprojects/libvfio-user.wrap in this series. > > Done: > https://gitlab.com/qemu-project/libvfio-user/-/commits/master > > Repository mirroring is automated now, so new upstream commits will > appear in the QEMU mirror repository from now on. > > > > > Finally, there is some more work required on top of this series to get > > message-based DMA to really work well: > > > > * libvfio-user has a long-standing issue where socket communication gets > > messed > > up when messages are sent from both ends at the same time. See > > https://github.com/nutanix/libvfio-user/issues/279 for more details. I've > > been engaging there and plan to contribute a fix. > > > > * qemu currently breaks down DMA accesses into chunks of size 8 bytes at > > maximum, each of which will be handled in a separate vfio-user DMA request > > message. This is quite terrible for large DMA acceses, such as when nvme > > reads and writes page-sized blocks for example. Thus, I would like to > > improve > > qemu to be able to perform larger accesses, at least for indirect memory > > regions. I have something working locally, but since this will likely > > result > > in more involved surgery and discussion, I am leaving this to be > > addressed in > > a separate patch. > > > > Mattias Nissler (3): > > softmmu: Support concurrent bounce buffers > > softmmu: Remove DMA unmap notification callback > > vfio-user: Message-based DMA support > > > > hw/remote/vfio-user-obj.c | 62 ++++++++++++++++-- > > softmmu/dma-helpers.c | 28 -------- > > softmmu/physmem.c | 131 ++++++++------------------------------ > > 3 files changed, 83 insertions(+), 138 deletions(-) > > Sorry for the late review. I was on vacation and am catching up on > emails. > > Paolo worked on the QEMU memory API and can give input on how to make > this efficient for large DMA accesses. There is a chance that memory > dispatch with larger sizes will be needed for ENQCMD CPU instruction > emulation too. > > Stefan
