Re: [Qemu-devel] [PATCH v2 0/7] Qemu virtio pmem device

[Wei Yang <richardw.yang@linux.intel.com>]

On Wed, Jun 19, 2019 at 03:19:00PM +0530, Pankaj Gupta wrote:
> This patch series has implementation for "virtio pmem"
> device. "virtio pmem" is persistent memory(nvdimm) device in 
> guest which allows to bypass the guest page cache. This
> also implements a VIRTIO based asynchronous flush mechanism.  
> Details of project idea for 'virtio pmem' flushing interface
> is shared [2] & [3].
>
> Sharing Qemu device emulation in this patchset. Tested with 
> guest kernel driver [1]. This series is based on David's 
> memory device refactoring [5] work with modified version of
> my initial virtio pmem [4] series.
>
> Usage: 
> ./qemu -name test -machine pc -m 8G,slots=240,maxmem=20G 
> -object memory-backend-file,id=mem1,share,mem-path=test.img,
>  size=4G,share
> -device virtio-pmem-pci,memdev=mem1,id=nv1
>

Hi, Pankaj

I tried this series with v14 kernel driver, while getting some error on using
this. Not sure this is my error configuration.

The qemu command line is:

    -object memory-backend-file,id=mem1,share=on,mem-path=/dev/dax0.0,size=1G,align=2M 
    -device virtio-pmem-pci,memdev=mem1,id=nv1

The guest boots up and I can see /dev/pmem0 device. But when I want to
partition this device, I got the error:

    # parted /dev/pmem0 mklabel gpt
    Warning: Error fsyncing/closing /dev/pmem0: Input/output error

Also I see an error when running "ndctl list":

    libndctl: __sysfs_device_parse: ndctl0: add_dev() failed

Would you mind letting me know which part I am wrong?

> (qemu) info memory-devices
>  Memory device [virtio-pmem]: "nv1"
>  memaddr: 0x240000000
>  size: 4294967296
>  memdev: /objects/mem1
>
> Implementation is divided into two parts:
> New virtio pmem guest driver and qemu code changes for new 
> virtio pmem paravirtualized device. In this series we are
> sharing Qemu device emulation.
>
>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. 
>
> Virtio-pmem security implications and suggested countermeasures:
> ---------------------------------------------------------------
>
> In previous posting of kernel driver, there was discussion [7]
> on possible implications of page cache side channel attacks with 
> virtio pmem. After thorough analysis of details of known side 
> channel attacks, below are the suggestions:
>
> - Depends entirely on how host backing image file is mapped 
>   into guest address space. 
>
> - virtio-pmem device emulation, by default shared mapping is used
>   to map host backing file. It is recommended to use separate
>   backing file at host side for every guest. This will prevent
>   any possibility of executing common code from multiple guests
>   and any chance of inferring guest local data based based on 
>   execution time.
>
> - If backing file is required to be shared among multiple guests 
>   it is recommended to don't support host page cache eviction 
>   commands from the guest driver. This will avoid any possibility
>   of inferring guest local data or host data from another guest. 
>
> - Proposed device specification [6] for virtio-pmem device with 
>   details of possible security implications and suggested 
>   countermeasures for device emulation.
>
>Changes from PATCH v1:
> - Change proposed version from qemu 4.0 to 4.1 - Eric
> - Remove virtio queue_add from unrealize function - Cornelia  
>
>[1] https://lkml.org/lkml/2019/6/12/624
>[2] https://www.spinics.net/lists/kvm/msg149761.html
>[3] https://www.spinics.net/lists/kvm/msg153095.html  
>[4] https://marc.info/?l=linux-kernel&m=153572228719237&w=2 
>[5] https://marc.info/?l=qemu-devel&m=153555721901824&w=2
>[6] https://lists.oasis-open.org/archives/virtio-dev/201903/msg00083.html
>[7] https://lkml.org/lkml/2019/1/9/1191
>
> Pankaj Gupta (3):
>  virtio-pmem: add virtio device
>  virtio-pmem: sync linux headers
>  virtio-pci: proxy for virtio-pmem
>
> David Hildenbrand (4):
>  virtio-pci: Allow to specify additional interfaces for the base type
>  hmp: Handle virtio-pmem when printing memory device infos
>  numa: Handle virtio-pmem in NUMA stats
>  pc: Support for virtio-pmem-pci
>
> hmp.c                                        |   27 ++-
> hw/i386/Kconfig                              |    1 
> hw/i386/pc.c                                 |   72 ++++++++++
> hw/virtio/Kconfig                            |   10 +
> hw/virtio/Makefile.objs                      |    2 
> hw/virtio/virtio-pci.c                       |    1 
> hw/virtio/virtio-pci.h                       |    1 
> hw/virtio/virtio-pmem-pci.c                  |  131 ++++++++++++++++++
> hw/virtio/virtio-pmem-pci.h                  |   34 ++++
> hw/virtio/virtio-pmem.c                      |  189 +++++++++++++++++++++++++++
> include/hw/pci/pci.h                         |    1 
> include/hw/virtio/virtio-pmem.h              |   49 +++++++
> include/standard-headers/linux/virtio_ids.h  |    1 
> include/standard-headers/linux/virtio_pmem.h |   35 +++++
> numa.c                                       |   24 +--
> qapi/misc.json                               |   28 +++-
> 16 files changed, 580 insertions(+), 26 deletions(-)
>----

-- 
Wei Yang
Help you, Help me