On 11/02/2016 12:09 PM, Alexey Kardashevskiy wrote: > On 02/11/16 14:29, Kirti Wankhede wrote: >> >> >> On 11/2/2016 6:54 AM, Alexey Kardashevskiy wrote: >>> On 02/11/16 01:01, Kirti Wankhede wrote: >>>> >>>> >>>> On 10/28/2016 7:48 AM, Alexey Kardashevskiy wrote: >>>>> On 27/10/16 23:31, Kirti Wankhede wrote: >>>>>> >>>>>> >>>>>> On 10/27/2016 12:50 PM, Alexey Kardashevskiy wrote: >>>>>>> On 18/10/16 08:22, Kirti Wankhede wrote: >>>>>>>> VFIO IOMMU drivers are designed for the devices which are IOMMU capable. >>>>>>>> Mediated device only uses IOMMU APIs, the underlying hardware can be >>>>>>>> managed by an IOMMU domain. >>>>>>>> >>>>>>>> Aim of this change is: >>>>>>>> - To use most of the code of TYPE1 IOMMU driver for mediated devices >>>>>>>> - To support direct assigned device and mediated device in single module >>>>>>>> >>>>>>>> Added two new callback functions to struct vfio_iommu_driver_ops. Backend >>>>>>>> IOMMU module that supports pining and unpinning pages for mdev devices >>>>>>>> should provide these functions. >>>>>>>> Added APIs for pining and unpining pages to VFIO module. These calls back >>>>>>>> into backend iommu module to actually pin and unpin pages. >>>>>>>> >>>>>>>> This change adds pin and unpin support for mediated device to TYPE1 IOMMU >>>>>>>> backend module. More details: >>>>>>>> - When iommu_group of mediated devices is attached, task structure is >>>>>>>> cached which is used later to pin pages and page accounting. >>>>>>> >>>>>>> >>>>>>> For SPAPR TCE IOMMU driver, I ended up caching mm_struct with >>>>>>> atomic_inc(&container->mm->mm_count) (patches are on the way) instead of >>>>>>> using @current or task as the process might be gone while VFIO container is >>>>>>> still alive and @mm might be needed to do proper cleanup; this might not be >>>>>>> an issue with this patchset now but still you seem to only use @mm from >>>>>>> task_struct. >>>>>>> >>>>>> >>>>>> Consider the example of QEMU process which creates VFIO container, QEMU >>>>>> in its teardown path would release the container. How could container be >>>>>> alive when process is gone? >>>>> >>>>> do_exit() in kernel/exit.c calls exit_mm() (which sets NULL to tsk->mm) >>>>> first, and then releases open files by calling exit_files(). So >>>>> container's release() does not have current->mm. >>>>> >>>> >>>> Incrementing usage count (get_task_struct()) while saving task structure >>>> and decementing it (put_task_struct()) from release() should work here. >>>> Updating the patch. >>> >>> I cannot see how the task->usage counter prevents do_exit() from performing >>> the exit, can you? >>> >> >> It will not prevent exit from do_exit(), but that will make sure that we >> don't have stale pointer of task structure. Then we can check whether >> the task is alive and get mm pointer in teardown path as below: > > > Or you could just reference and use @mm as KVM and others do. Or there is > anything else you need from @current than just @mm? > I agree. If @mm is the only thing needed, there is really no reason to refer to the @task :-) -- Thanks, Jike -- 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
