Re: [PATCH v7 00/12] iommu: Prepare to deliver page faults to user space

[Baolu Lu <baolu.lu@linux.intel.com>]

On 2023/11/24 14:30, liulongfang wrote:
> On 2023/11/15 11:02, Lu Baolu Wrote:
>> When a user-managed page table is attached to an IOMMU, it is necessary
>> to deliver IO page faults to user space so that they can be handled
>> appropriately. One use case for this is nested translation, which is
>> currently being discussed in the mailing list.
>>
>> I have posted a RFC series [1] that describes the implementation of
>> delivering page faults to user space through IOMMUFD. This series has
>> received several comments on the IOMMU refactoring, which I am trying to
>> address in this series.
>>
>> The major refactoring includes:
>>
>> - [PATCH 01 ~ 04] Move include/uapi/linux/iommu.h to
>>    include/linux/iommu.h. Remove the unrecoverable fault data definition.
>> - [PATCH 05 ~ 06] Remove iommu_[un]register_device_fault_handler().
>> - [PATCH 07 ~ 10] Separate SVA and IOPF. Make IOPF a generic page fault
>>    handling framework.
>> - [PATCH 11 ~ 12] Improve iopf framework for iommufd use.
>>
>> This is also available at github [2].
>>
>> [1] https://lore.kernel.org/linux-iommu/20230530053724.232765-1-baolu.lu@linux.intel.com/
>> [2] https://github.com/LuBaolu/intel-iommu/commits/preparatory-io-pgfault-delivery-v7
>>
>> Change log:
>> v7:
>>   - Rebase to v6.7-rc1.
>>   - Export iopf_group_response() for global use.
>>   - Release lock when calling iopf handler.
>>   - The whole series has been verified to work for SVA case on Intel
>>     platforms by Zhao Yan. Add her Tested-by to affected patches.
>>
>> v6: https://lore.kernel.org/linux-iommu/20230928042734.16134-1-baolu.lu@linux.intel.com/
>>   - [PATCH 09/12] Check IS_ERR() against the iommu domain. [Jingqi/Jason]
>>   - [PATCH 12/12] Rename the comments and name of iopf_queue_flush_dev(),
>>     no functionality changes. [Kevin]
>>   - All patches rebased on the latest iommu/core branch.
>>
>> v5: https://lore.kernel.org/linux-iommu/20230914085638.17307-1-baolu.lu@linux.intel.com/
>>   - Consolidate per-device fault data management. (New patch 11)
>>   - Improve iopf_queue_flush_dev(). (New patch 12)
>>
>> v4: https://lore.kernel.org/linux-iommu/20230825023026.132919-1-baolu.lu@linux.intel.com/
>>   - Merge iommu_fault_event and iopf_fault. They are duplicate.
>>   - Move iommu_report_device_fault() and iommu_page_response() to
>>     io-pgfault.c.
>>   - Move iommu_sva_domain_alloc() to iommu-sva.c.
>>   - Add group->domain and use it directly in sva fault handler.
>>   - Misc code refactoring and refining.
>>
>> v3: https://lore.kernel.org/linux-iommu/20230817234047.195194-1-baolu.lu@linux.intel.com/
>>   - Convert the fault data structures from uAPI to kAPI.
>>   - Merge iopf_device_param into iommu_fault_param.
>>   - Add debugging on domain lifetime for iopf.
>>   - Remove patch "iommu: Change the return value of dev_iommu_get()".
>>   - Remove patch "iommu: Add helper to set iopf handler for domain".
>>   - Misc code refactoring and refining.
>>
>> v2: https://lore.kernel.org/linux-iommu/20230727054837.147050-1-baolu.lu@linux.intel.com/
>>   - Remove unrecoverable fault data definition as suggested by Kevin.
>>   - Drop the per-device fault cookie code considering that doesn't make
>>     much sense for SVA.
>>   - Make the IOMMU page fault handling framework generic. So that it can
>>     available for use cases other than SVA.
>>
>> v1: https://lore.kernel.org/linux-iommu/20230711010642.19707-1-baolu.lu@linux.intel.com/
>>
>> Lu Baolu (12):
>>    iommu: Move iommu fault data to linux/iommu.h
>>    iommu/arm-smmu-v3: Remove unrecoverable faults reporting
>>    iommu: Remove unrecoverable fault data
>>    iommu: Cleanup iopf data structure definitions
>>    iommu: Merge iopf_device_param into iommu_fault_param
>>    iommu: Remove iommu_[un]register_device_fault_handler()
>>    iommu: Merge iommu_fault_event and iopf_fault
>>    iommu: Prepare for separating SVA and IOPF
>>    iommu: Make iommu_queue_iopf() more generic
>>    iommu: Separate SVA and IOPF
>>    iommu: Consolidate per-device fault data management
>>    iommu: Improve iopf_queue_flush_dev()
>>
>>   include/linux/iommu.h                         | 266 +++++++---
>>   drivers/iommu/intel/iommu.h                   |   2 +-
>>   drivers/iommu/iommu-sva.h                     |  71 ---
>>   include/uapi/linux/iommu.h                    | 161 ------
>>   .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  14 +-
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   |  51 +-
>>   drivers/iommu/intel/iommu.c                   |  25 +-
>>   drivers/iommu/intel/svm.c                     |   8 +-
>>   drivers/iommu/io-pgfault.c                    | 469 ++++++++++++------
>>   drivers/iommu/iommu-sva.c                     |  66 ++-
>>   drivers/iommu/iommu.c                         | 232 ---------
>>   MAINTAINERS                                   |   1 -
>>   drivers/iommu/Kconfig                         |   4 +
>>   drivers/iommu/Makefile                        |   3 +-
>>   drivers/iommu/intel/Kconfig                   |   1 +
>>   15 files changed, 601 insertions(+), 773 deletions(-)
>>   delete mode 100644 drivers/iommu/iommu-sva.h
>>   delete mode 100644 include/uapi/linux/iommu.h
>>
> 
> Tested-By: Longfang Liu <liulongfang@huawei.com>

Thank you for the testing.

> 
> The Arm SVA mode based on HiSilicon crypto accelerator completed the functional test
> and performance test of page fault scenarios.
> 1. The IOMMU page fault processing function is normal.
> 2. Performance test on 128 core ARM platform. performance is reduced:
> 
> Threads  Performance
> 8         -0.77%
> 16        -1.1%
> 32        -0.31%
> 64        -0.49%
> 128       -0.72%
> 256       -1.7%
> 384       -4.94%
> 512       NA（iopf timeout）
> 
> Finally, continuing to increase the number of threads will cause iommu's page fault
> processing to time out(more than 4.2 seconds).
> This problem occurs both in the before version(kernel6.7-rc1) and
> in the after modification's version.

Probably you can check whether commit 6bbd42e2df8f ("mmu_notifiers: call
invalidate_range() when invalidating TLBs") matters.

It was discussed in this thread.

https://lore.kernel.org/linux-iommu/20231117090933.75267-1-baolu.lu@linux.intel.com/

Best regards,
baolu