We are sharing RFC version of 'fake DAX' flushing interface for feedback. This is still work in progress and not yet ready for merging. Prototype implements two major parts: - Qemu virtio-pmem device It exposes a persistent memory range to KVM guest which at host side is file backed memory and works as persistent memory device. In addition to this it provides a virtio flushing interface for KVM guest to do a Qemu side sync for guest DAX persistent memory range. - Guest virtio-pmem driver Reads persistent memory range from paravirt device and registers with 'nvdimm_bus'. 'nvdimm/pmem' driver uses this information to allocate persistent memory range. Also, we have implemented guest side of VIRTIO flushing interface. Changes from previous RFC: - Reuse existing 'pmem' code instead of creating an entirely new block driver. - Use VIRTIO driver to register memory information with nvdimm_bus and create region_type accordingly. - Use VIRTIO flushing interface from existing pmem driver code based on registered flushign mechanism. We have done the implementation based on suggestions here [1]. Previous RFC is shared here [2]. Details of project idea for 'fake DAX' flushing is shared here [3] & [4]. [1] https://marc.info/?l=linux-mm&m=150782346802290&w=2 [2] https://marc.info/?l=kvm&m=151630416506527&w=2 [3] https://www.spinics.net/lists/kvm/msg149761.html [4] https://www.spinics.net/lists/kvm/msg153095.html Work yet to be done: - Qemu RAM address handling independent of PC-DIMM so that memory operations(get_free_address) can be used for VIRTIO device type as well. (David Hildenbrand CCed has a prototype for this). - Qemu device flush functionality trigger with guest fsync on file. - Qemu live migration work when host page cache is used. - Multiple virtio-pmem disks support. - Prepare virtio spec after we get feedback on current approach. drivers/nvdimm/region_devs.c | 7 ++ drivers/virtio/Kconfig | 12 +++ drivers/virtio/Makefile | 1 drivers/virtio/virtio_pmem.c | 122 +++++++++++++++++++++++++++++++++++++++ include/linux/libnvdimm.h | 2 include/uapi/linux/virtio_ids.h | 1 include/uapi/linux/virtio_pmem.h | 61 +++++++++++++++++++ 7 files changed, 206 insertions(+)
