This patch series has implementation for "virtio pmem".
"virtio pmem" is fake persistent memory(nvdimm) in guest
which allows to bypass the guest page cache. This also
implements a VIRTIO based asynchronous flush mechanism.
Sharing guest kernel driver in this patchset with the
changes suggested in v2. Tested with Qemu side device
emulation for virtio-pmem [6].
Details of project idea for 'virtio pmem' flushing interface
is shared [3] & [4].
Implementation is divided into two parts:
New virtio pmem guest driver and qemu code changes for new
virtio pmem paravirtualized device.
1. Guest virtio-pmem kernel driver
---------------------------------
- Reads persistent memory range from paravirt device and
registers with 'nvdimm_bus'.
- 'nvdimm/pmem' driver uses this information to allocate
persistent memory region and setup filesystem operations
to the allocated memory.
- virtio pmem driver implements asynchronous flushing
interface to flush from guest to host.
2. Qemu virtio-pmem device
---------------------------------
- Creates virtio pmem device and exposes a memory range to
KVM guest.
- At host side this is file backed memory which acts as
persistent memory.
- Qemu side flush uses aio thread pool API's and virtio
for asynchronous guest multi request handling.
David Hildenbrand CCed also posted a modified version[6] of
qemu virtio-pmem code based on updated Qemu memory device API.
Virtio-pmem errors handling:
----------------------------------------
Checked behaviour of virtio-pmem for below types of errors
Need suggestions on expected behaviour for handling these errors?
- Hardware Errors: Uncorrectable recoverable Errors:
a] virtio-pmem:
- As per current logic if error page belongs to Qemu process,
host MCE handler isolates(hwpoison) that page and send SIGBUS.
Qemu SIGBUS handler injects exception to KVM guest.
- KVM guest then isolates the page and send SIGBUS to guest
userspace process which has mapped the page.
b] Existing implementation for ACPI pmem driver:
- Handles such errors with MCE notifier and creates a list
of bad blocks. Read/direct access DAX operation return EIO
if accessed memory page fall in bad block list.
- It also starts backgound scrubbing.
- Similar functionality can be reused in virtio-pmem with MCE
notifier but without scrubbing(no ACPI/ARS)? Need inputs to
confirm if this behaviour is ok or needs any change?
Changes from PATCH v2: [1]
- Disable MAP_SYNC for ext4 & XFS filesystems - [Dan]
- Use name 'virtio pmem' in place of 'fake dax'
Changes from PATCH v1: [2]
- 0-day build test for build dependency on libnvdimm
Changes suggested by - [Dan Williams]
- Split the driver into two parts virtio & pmem
- Move queuing of async block request to block layer
- Add "sync" parameter in nvdimm_flush function
- Use indirect call for nvdimm_flush
- Don’t move declarations to common global header e.g nd.h
- nvdimm_flush() return 0 or -EIO if it fails
- Teach nsio_rw_bytes() that the flush can fail
- Rename nvdimm_flush() to generic_nvdimm_flush()
- Use 'nd_region->provider_data' for long dereferencing
- Remove virtio_pmem_freeze/restore functions
- Remove BSD license text with SPDX license text
- Add might_sleep() in virtio_pmem_flush - [Luiz]
- Make spin_lock_irqsave() narrow
Changes from RFC v3
- Rebase to latest upstream - Luiz
- Call ndregion->flush in place of nvdimm_flush- Luiz
- kmalloc return check - Luiz
- virtqueue full handling - Stefan
- Don't map entire virtio_pmem_req to device - Stefan
- request leak, correct sizeof req- Stefan
- Move declaration to virtio_pmem.c
Changes from RFC v2:
- Add flush function in the nd_region in place of switching
on a flag - Dan & Stefan
- Add flush completion function with proper locking and wait
for host side flush completion - Stefan & Dan
- Keep userspace API in uapi header file - Stefan, MST
- Use LE fields & New device id - MST
- Indentation & spacing suggestions - MST & Eric
- Remove extra header files & add licensing - Stefan
Changes from RFC v1:
- Reuse existing 'pmem' code for registering persistent
memory and other operations instead of creating an entirely
new block driver.
- Use VIRTIO driver to register memory information with
nvdimm_bus and create region_type accordingly.
- Call VIRTIO flush from existing pmem driver.
Pankaj Gupta (5):
libnvdimm: nd_region flush callback support
virtio-pmem: Add virtio-pmem guest driver
libnvdimm: add nd_region buffered dax_dev flag
ext4: disable map_sync for virtio pmem
xfs: disable map_sync for virtio pmem
[2] https://lkml.org/lkml/2018/8/31/407
[3] https://www.spinics.net/lists/kvm/msg149761.html
[4] https://www.spinics.net/lists/kvm/msg153095.html
[5] https://lkml.org/lkml/2018/8/31/413
[6] https://marc.info/?l=qemu-devel&m=153555721901824&w=2
drivers/acpi/nfit/core.c | 4 -
drivers/dax/super.c | 17 +++++
drivers/nvdimm/claim.c | 6 +
drivers/nvdimm/nd.h | 1
drivers/nvdimm/pmem.c | 15 +++-
drivers/nvdimm/region_devs.c | 45 +++++++++++++-
drivers/nvdimm/virtio_pmem.c | 84 ++++++++++++++++++++++++++
drivers/virtio/Kconfig | 10 +++
drivers/virtio/Makefile | 1
drivers/virtio/pmem.c | 125 +++++++++++++++++++++++++++++++++++++++
fs/ext4/file.c | 11 +++
fs/xfs/xfs_file.c | 8 ++
include/linux/dax.h | 9 ++
include/linux/libnvdimm.h | 11 +++
include/linux/virtio_pmem.h | 60 ++++++++++++++++++
include/uapi/linux/virtio_ids.h | 1
include/uapi/linux/virtio_pmem.h | 10 +++
17 files changed, 406 insertions(+), 12 deletions(-)
