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Re: [PATCH v14 09/22] vfio iommu type1: Add task structure to vfio_dma

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On Thu, 17 Nov 2016 16:41:14 +1100
Alexey Kardashevskiy <aik@ozlabs.ru> wrote:

> On 17/11/16 07:46, Kirti Wankhede wrote:
> > Add task structure to vfio_dma structure. Task structure is used for:
> > - During DMA_UNMAP, same task who mapped it or other task who shares same
> > address space is allowed to unmap, otherwise unmap fails.
> > QEMU maps few iova ranges initially, then fork threads and from the child
> > thread calls DMA_UNMAP on previously mapped iova. Since child shares same
> > address space, DMA_UNMAP is successful.
> > - Avoid accessing struct mm while process is exiting by acquiring
> > reference of task's mm during page accounting.
> > - It is also used to get task mlock capability and rlimit for mlock.
> > 
> > Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
> > Signed-off-by: Neo Jia <cjia@nvidia.com>
> > Reviewed-by: Dong Jia Shi <bjsdjshi@linux.vnet.ibm.com>  
> 
> 
> I keep whinging that @mm should be referenced, not @current but you keep
> referencing @current even if you only need @mm and you are not telling why
> - and I am wondering what I am missing here? Something else will be used
> from @task later, besides just @mm?

Yes, we reference @current from vfio_dma_do_map() and this is stored
on the struct vfio_dma.  A reference to current is held because the
external page pinning in vfio_pin_page_external() needs to test the
capabilities of the task for CAP_IPC_LOCK to know whether locked memory
limits are in effect for the task even when it's not @current (ie. an
asynchronous call from the vendor driver regardless of what task is
currently running).  There are also various get_task_mm() taken
temporarily when we're working with the mm of that task.  Do you spot
any issues with this behavior? Thanks,

Alex

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[PATCH v14 00/22] Add Mediated device support Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
  [PATCH v14 11/22] vfio iommu: Add blocking notifier to notify DMA_UNMAP Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
    Re: [PATCH v14 11/22] vfio iommu: Add blocking notifier to notify  DMA_UNMAP Alex Williamson <alex.williamson@redhat.com> - 2016-11-17 01:10 +0100
    Re: [PATCH v14 11/22] vfio iommu: Add blocking notifier to notify  DMA_UNMAP Jike Song <jike.song@intel.com> - 2016-11-17 04:00 +0100
    Re: [PATCH v14 11/22] vfio iommu: Add blocking notifier to notify DMA_UNMAP Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-17 06:00 +0100
  [PATCH v14 18/22] vfio: Define device_api strings Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
  [PATCH v14 09/22] vfio iommu type1: Add task structure to vfio_dma Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
    Re: [PATCH v14 09/22] vfio iommu type1: Add task structure to  vfio_dma Alexey Kardashevskiy <aik@ozlabs.ru> - 2016-11-17 06:50 +0100
      Re: [PATCH v14 09/22] vfio iommu type1: Add task structure to  vfio_dma Alex Williamson <alex.williamson@redhat.com> - 2016-11-17 07:20 +0100
        Re: [PATCH v14 09/22] vfio iommu type1: Add task structure to  vfio_dma Alexey Kardashevskiy <aik@ozlabs.ru> - 2016-11-17 07:50 +0100
      Re: [PATCH v14 09/22] vfio iommu type1: Add task structure to  vfio_dma Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-17 07:30 +0100
  [PATCH v14 07/22] vfio iommu type1: Update argument of vaddr_get_pfn() Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
  [PATCH v14 20/22] docs: Sysfs ABI for mediated device framework Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
  [PATCH v14 13/22] vfio: Introduce common function to add capabilities Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
    Re: [Qemu-devel] [PATCH v14 13/22] vfio: Introduce common function to  add capabilities Auger Eric <eric.auger@redhat.com> - 2016-11-21 12:10 +0100
  [PATCH v14 01/22] vfio: Mediated device Core driver Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 21:50 +0100
  [PATCH v14 03/22] vfio: Rearrange functions to get vfio_group from dev Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 22:00 +0100
  [PATCH v14 08/22] vfio iommu type1: Add find_iommu_group() function Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 22:00 +0100
    Re: [PATCH v14 08/22] vfio iommu type1: Add find_iommu_group()  function Auger Eric <eric.auger@redhat.com> - 2016-11-21 12:30 +0100
      Re: [PATCH v14 08/22] vfio iommu type1: Add find_iommu_group()  function Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-21 13:00 +0100
        Re: [PATCH v14 08/22] vfio iommu type1: Add find_iommu_group()  function Auger Eric <eric.auger@redhat.com> - 2016-11-21 13:50 +0100
  [PATCH v14 02/22] vfio: VFIO based driver for Mediated devices Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 22:00 +0100
  [PATCH v14 12/22] vfio: Add notifier callback to parent's ops structure of mdev Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 22:00 +0100
    Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops  structure of mdev Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-17 06:10 +0100
    Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops structure of mdev Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-17 06:10 +0100
    Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops  structure of mdev Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-17 18:30 +0100
      Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops  structure of mdev Alex Williamson <alex.williamson@redhat.com> - 2016-11-17 18:40 +0100
    Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops  structure of mdev Jike Song <jike.song@intel.com> - 2016-11-17 18:40 +0100
      Re: [PATCH v14 12/22] vfio: Add notifier callback to parent's ops  structure of mdev Alex Williamson <alex.williamson@redhat.com> - 2016-11-17 19:00 +0100
  [PATCH v14 04/22] vfio: Common function to increment container_users Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-16 22:00 +0100
  Re: [PATCH v14 00/22] Add Mediated device support Alex Williamson <alex.williamson@redhat.com> - 2016-11-17 22:30 +0100
    Re: [PATCH v14 00/22] Add Mediated device support Neo Jia <cjia@nvidia.com> - 2016-11-17 23:20 +0100
      Re: [PATCH v14 00/22] Add Mediated device support Kirti Wankhede <kwankhede@nvidia.com> - 2016-11-18 03:10 +0100
        Re: [Qemu-devel] [PATCH v14 00/22] Add Mediated device support Jike Song <jike.song@intel.com> - 2016-11-18 03:30 +0100
    RE: [PATCH v14 00/22] Add Mediated device support "Tian, Kevin" <kevin.tian@intel.com> - 2016-11-18 00:30 +0100
      Re: [PATCH v14 00/22] Add Mediated device support Alex Williamson <alex.williamson@redhat.com> - 2016-11-18 01:00 +0100
        Re: [PATCH v14 00/22] Add Mediated device support Zhenyu Wang <zhenyuw@linux.intel.com> - 2016-11-18 10:30 +0100
          Re: [PATCH v14 00/22] Add Mediated device support Alex Williamson <alex.williamson@redhat.com> - 2016-11-18 16:50 +0100
            Re: [PATCH v14 00/22] Add Mediated device support Daniel Vetter <daniel@ffwll.ch> - 2016-11-18 17:20 +0100
              Re: [PATCH v14 00/22] Add Mediated device support Alex Williamson <alex.williamson@redhat.com> - 2016-11-18 18:00 +0100

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