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? -- Alexey -- 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
