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Re: [Qemu-devel] [PATCH v14 09/22] vfio iommu type1: Add task structure
From: |
Alex Williamson |
Subject: |
Re: [Qemu-devel] [PATCH v14 09/22] vfio iommu type1: Add task structure to vfio_dma |
Date: |
Wed, 16 Nov 2016 23:12:06 -0700 |
On Thu, 17 Nov 2016 16:41:14 +1100
Alexey Kardashevskiy <address@hidden> 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 <address@hidden>
> > Signed-off-by: Neo Jia <address@hidden>
> > Reviewed-by: Dong Jia Shi <address@hidden>
>
>
> 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
- [Qemu-devel] [PATCH v14 00/22] Add Mediated device support, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 02/22] vfio: VFIO based driver for Mediated devices, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 03/22] vfio: Rearrange functions to get vfio_group from dev, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 01/22] vfio: Mediated device Core driver, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 05/22] vfio iommu: Added pin and unpin callback functions to vfio_iommu_driver_ops, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 06/22] vfio iommu type1: Update arguments of vfio_lock_acct, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 08/22] vfio iommu type1: Add find_iommu_group() function, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 04/22] vfio: Common function to increment container_users, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 09/22] vfio iommu type1: Add task structure to vfio_dma, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 10/22] vfio iommu type1: Add support for mediated devices, Kirti Wankhede, 2016/11/16
- [Qemu-devel] [PATCH v14 12/22] vfio: Add notifier callback to parent's ops structure of mdev, Kirti Wankhede, 2016/11/16