On Thu, 17 Nov 2016 16:41:14 +1100 Alexey Kardashevskiy <aik@xxxxxxxxx> 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@xxxxxxxxxx> > > Signed-off-by: Neo Jia <cjia@xxxxxxxxxx> > > Reviewed-by: Dong Jia Shi <bjsdjshi@xxxxxxxxxxxxxxxxxx> > > > 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 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
