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SubjectRe: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device


Please ignore this series as my network went down while
sending this. I will send this series again.

Thanks,
Pankaj

>
> 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(-)
>
>
>

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