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 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 a fix is in review. * 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 accesses, 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. Changes from v1: * Address Stefan's review comments. In particular, enforce an allocation limit and don't drop the map client callbacks given that map requests can fail when hitting size limits. * libvfio-user version bump now included in the series. * Tested as well on big-endian s390x. This uncovered another byte order issue in vfio-user server code that I've included a fix for. Mattias Nissler (4): softmmu: Support concurrent bounce buffers Update subprojects/libvfio-user vfio-user: Message-based DMA support vfio-user: Fix config space access byte order hw/remote/trace-events | 2 + hw/remote/vfio-user-obj.c | 88 +++++++++++++++++++++++++++++++---- include/sysemu/sysemu.h | 2 + qemu-options.hx | 27 +++++++++++ softmmu/globals.c | 1 + softmmu/physmem.c | 84 ++++++++++++++++++--------------- softmmu/vl.c | 6 +++ subprojects/libvfio-user.wrap | 2 +- 8 files changed, 165 insertions(+), 47 deletions(-) -- 2.34.1
