[PATCH v2 4/4] drm/i915: convert get_user_pages() --> pin_user_pages()

John Hubbard
2020-05-22T05:19:48Z

This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
https://lwn.net/Articles/807108/

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
drivers/gpu/drm/i915/gem/i915_gem_userptr.c | 22 ++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
index 7ffd7afeb7a5..b55ac7563189 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_userptr.c
@@ -471,7 +471,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
down_read(&mm->mmap_sem);
locked = 1;
}
- ret = get_user_pages_remote
+ ret = pin_user_pages_remote
(work->task, mm,
obj->userptr.ptr + pinned * PAGE_SIZE,
npages - pinned,
@@ -507,7 +507,7 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
}
mutex_unlock(&obj->mm.lock);

- release_pages(pvec, pinned);
+ unpin_user_pages(pvec, pinned);
kvfree(pvec);

i915_gem_object_put(obj);
@@ -564,6 +564,7 @@ static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
struct sg_table *pages;
bool active;
int pinned;
+ unsigned int gup_flags = 0;

/* If userspace should engineer that these pages are replaced in
* the vma between us binding this page into the GTT and completion
@@ -598,11 +599,14 @@ static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
GFP_KERNEL |
__GFP_NORETRY |
__GFP_NOWARN);
- if (pvec) /* defer to worker if malloc fails */
- pinned = __get_user_pages_fast(obj->userptr.ptr,
- num_pages,
- !i915_gem_object_is_readonly(obj),
- pvec);
+ /* defer to worker if malloc fails */
+ if (pvec) {
+ if (!i915_gem_object_is_readonly(obj))
+ gup_flags |= FOLL_WRITE;
+ pinned = pin_user_pages_fast_only(obj->userptr.ptr,
+ num_pages, gup_flags,
+ pvec);
+ }
}

active = false;
@@ -620,7 +624,7 @@ static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
__i915_gem_userptr_set_active(obj, true);

if (IS_ERR(pages))
- release_pages(pvec, pinned);
+ unpin_user_pages(pvec, pinned);
kvfree(pvec);

return PTR_ERR_OR_ZERO(pages);
@@ -675,7 +679,7 @@ i915_gem_userptr_put_pages(struct drm_i915_gem_object *obj,
}

mark_page_accessed(page);
- put_page(page);
+ unpin_user_page(page);
}
obj->mm.dirty = false;

--
2.26.2