Re: [RFC PATCH v3 0/8] Add IOPF support for VFIO passthrough

[Shenming Lu]

On 2021/4/9 11:44, Shenming Lu wrote:
> Hi,
> 
> Requesting for your comments and suggestions. :-)

Kind ping...

> 
> The static pinning and mapping problem in VFIO and possible solutions
> have been discussed a lot [1, 2]. One of the solutions is to add I/O
> Page Fault support for VFIO devices. Different from those relatively
> complicated software approaches such as presenting a vIOMMU that provides
> the DMA buffer information (might include para-virtualized optimizations),
> IOPF mainly depends on the hardware faulting capability, such as the PCIe
> PRI extension or Arm SMMU stall model. What's more, the IOPF support in
> the IOMMU driver has already been implemented in SVA [3]. So we add IOPF
> support for VFIO passthrough based on the IOPF part of SVA in this series.
> 
> We have measured its performance with UADK [4] (passthrough an accelerator
> to a VM(1U16G)) on Hisilicon Kunpeng920 board (and compared with host SVA):
> 
> Run hisi_sec_test...
>  - with varying sending times and message lengths
>  - with/without IOPF enabled (speed slowdown)
> 
> when msg_len = 1MB (and PREMAP_LEN (in Patch 4) = 1):
>             slowdown (num of faults)
>  times      VFIO IOPF      host SVA
>  1          63.4% (518)    82.8% (512)
>  100        22.9% (1058)   47.9% (1024)
>  1000       2.6% (1071)    8.5% (1024)
> 
> when msg_len = 10MB (and PREMAP_LEN = 512):
>             slowdown (num of faults)
>  times      VFIO IOPF
>  1          32.6% (13)
>  100        3.5% (26)
>  1000       1.6% (26)
> 
> History:
> 
> v2 -> v3
>  - Nit fixes.
>  - No reason to disable reporting the unrecoverable faults. (baolu)
>  - Maintain a global IOPF enabled group list.
>  - Split the pre-mapping optimization to be a separate patch.
>  - Add selective faulting support (use vfio_pin_pages to indicate the
>    non-faultable scope and add a new struct vfio_range to record it,
>    untested). (Kevin)
> 
> v1 -> v2
>  - Numerous improvements following the suggestions. Thanks a lot to all
>    of you.
> 
> Note that PRI is not supported at the moment since there is no hardware.
> 
> Links:
> [1] Lesokhin I, et al. Page Fault Support for Network Controllers. In ASPLOS,
>     2016.
> [2] Tian K, et al. coIOMMU: A Virtual IOMMU with Cooperative DMA Buffer Tracking
>     for Efficient Memory Management in Direct I/O. In USENIX ATC, 2020.
> [3] https://patchwork.kernel.org/project/linux-arm-kernel/cover/20210401154718.307519-1-jean-philippe@xxxxxxxxxx/
> [4] https://github.com/Linaro/uadk
> 
> Thanks,
> Shenming
> 
> 
> Shenming Lu (8):
>   iommu: Evolve the device fault reporting framework
>   vfio/type1: Add a page fault handler
>   vfio/type1: Add an MMU notifier to avoid pinning
>   vfio/type1: Pre-map more pages than requested in the IOPF handling
>   vfio/type1: VFIO_IOMMU_ENABLE_IOPF
>   vfio/type1: No need to statically pin and map if IOPF enabled
>   vfio/type1: Add selective DMA faulting support
>   vfio: Add nested IOPF support
> 
>  .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |    3 +-
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |   18 +-
>  drivers/iommu/iommu.c                         |   56 +-
>  drivers/vfio/vfio.c                           |   85 +-
>  drivers/vfio/vfio_iommu_type1.c               | 1000 ++++++++++++++++-
>  include/linux/iommu.h                         |   19 +-
>  include/linux/vfio.h                          |   13 +
>  include/uapi/linux/iommu.h                    |    4 +
>  include/uapi/linux/vfio.h                     |    6 +
>  9 files changed, 1181 insertions(+), 23 deletions(-)
>