From eba0b87184e2d8361741f2e113137886bd5eb10d Mon Sep 17 00:00:00 2001
From: Chris Wilson <chris@chris-wilson.co.uk>
Date: Mon, 11 Nov 2019 13:32:04 +0000
Subject: drm/i915/userptr: Handle unlocked gup retries
Git-commit: d323c9b88260bc2cf3e3ed4bc741ab69643e0233
Patch-mainline: v5.6-rc1
References: jsc#SLE-12680, jsc#SLE-12880, jsc#SLE-12882, jsc#SLE-12883, jsc#SLE-13496, jsc#SLE-15322

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: 5b56d49fc31d ("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
Signed-off-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index a68b8445ebb3..57fc635cec1a 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -460,26 +460,31 @@ __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;
 			}
-			up_read(&mm->mmap_sem);
+			if (locked)
+				up_read(&mm->mmap_sem);
 			mmput(mm);
 		}
 	}
-- 
2.28.0