Commit d323c9b8 authored Nov 11, 2019 by Chris Wilson

drm/i915/userptr: Handle unlocked gup retries



Enable gup to retry and fault the pages outside of the mmap_sem lock in
our worker. As we are inside our worker, outside of any critical path,
we can allow the mmap_sem lock to be dropped in order to service a page
fault; this in turn allows the mm to populate the page using a slow
fault handler.

References: 5b56d49f ("mm: add locked parameter to get_user_pages_remote()")
Testcase: igt/gem_userptr/userfault
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191111133205.11590-2-chris@chris-wilson.co.uk

parent 0d4bbe3d

drivers/gpu/drm/i915/gem/i915_gem_userptr.c

+8 −3

Original line number	Diff line number	Diff line
		@@ -459,25 +459,30 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
		if (pvec != NULL) {
		struct mm_struct *mm = obj->userptr.mm->mm;
		unsigned int flags = 0;
		int locked = 0;

		if (!i915_gem_object_is_readonly(obj))
		flags \|= FOLL_WRITE;

		ret = -EFAULT;
		if (mmget_not_zero(mm)) {
		down_read(&mm->mmap_sem);
		while (pinned < npages) {
		if (!locked) {
		down_read(&mm->mmap_sem);
		locked = 1;
		}
		ret = get_user_pages_remote
		(work->task, mm,
		obj->userptr.ptr + pinned * PAGE_SIZE,
		npages - pinned,
		flags,
		pvec + pinned, NULL, NULL);
		pvec + pinned, NULL, &locked);
		if (ret < 0)
		break;

		pinned += ret;
		}
		if (locked)
		up_read(&mm->mmap_sem);
		mmput(mm);
		}

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