linux-kernel - Re: [RFC v3 0/2] kvm "fake DAX" device flushing

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Date:   Tue, 28 Aug 2018 14:13:24 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Pankaj Gupta <pagupta@...hat.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, qemu-devel@...gnu.org,
        linux-nvdimm@...1.01.org
Cc:     jack@...e.cz, stefanha@...hat.com, dan.j.williams@...el.com,
        riel@...riel.com, haozhong.zhang@...el.com, nilal@...hat.com,
        kwolf@...hat.com, pbonzini@...hat.com, ross.zwisler@...el.com,
        xiaoguangrong.eric@...il.com, hch@...radead.org, mst@...hat.com,
        niteshnarayanlal@...mail.com, lcapitulino@...hat.com,
        imammedo@...hat.com, eblake@...hat.com
Subject: Re: [RFC v3 0/2] kvm "fake DAX" device flushing

On 13.07.2018 09:52, Pankaj Gupta wrote:
> This is RFC V3 for 'fake DAX' flushing interface sharing
> for review. This patchset has two parts:
> 
> - Guest virtio-pmem driver
>   Guest 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.
> 
> - 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 virtio device handling of flushing 
>   interface. KVM guest performs Qemu side asynchronous sync using 
>   this interface.
> 
> 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.
> 
> Details of project idea for 'fake DAX' flushing interface is 
> shared [2] & [3].
> 
> Pankaj Gupta (2):
>    Add virtio-pmem guest driver
>    pmem: device flush over VIRTIO
> 
> [1] https://marc.info/?l=linux-mm&m=150782346802290&w=2
> [2] https://www.spinics.net/lists/kvm/msg149761.html
> [3] https://www.spinics.net/lists/kvm/msg153095.html  
> 
>  drivers/nvdimm/nd.h              |    1 
>  drivers/nvdimm/pmem.c            |    4 
>  drivers/nvdimm/region_devs.c     |   24 +++-
>  drivers/virtio/Kconfig           |    9 +
>  drivers/virtio/Makefile          |    1 
>  drivers/virtio/virtio_pmem.c     |  190 +++++++++++++++++++++++++++++++++++++++
>  include/linux/libnvdimm.h        |    5 -
>  include/linux/virtio_pmem.h      |   44 +++++++++
>  include/uapi/linux/virtio_ids.h  |    1 
>  include/uapi/linux/virtio_pmem.h |   40 ++++++++
>  10 files changed, 310 insertions(+), 9 deletions(-)
> 

Hi Pankaj,

do you have a branch for the QEMU part somewhere available? I want to
see how this works with MemoryDevice changes.

-- 

Thanks,

David / dhildenb