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. 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(-) -- 2.34.1
