mm/frame-vector: Use FOLL_LONGTERM

This is used by media/videbuf2 for persistent dma mappings, not just
for a single dma operation and then freed again, so needs
FOLL_LONGTERM.

Unfortunately current pup_locked doesn't support FOLL_LONGTERM due to
locking issues. Rework the code to pull the pup path out from the
mmap_sem critical section as suggested by Jason.

By relying entirely on the vma checks in pin_user_pages and follow_pfn
(for vm_flags and vma_is_fsdax) we can also streamline the code a lot.

Note that pin_user_pages_fast is a safe replacement despite the
seeming lack of checking for vma->vm_flasg & (VM_IO | VM_PFNMAP). Such
ptes are marked with pte_mkspecial (which pup_fast rejects in the
fastpath), and only architectures supporting that support the
pin_user_pages_fast fastpath.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Pawel Osciak <pawel@osciak.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Tomasz Figa <tfiga@chromium.org>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: linux-mm@kvack.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-samsung-soc@vger.kernel.org
Cc: linux-media@vger.kernel.org
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201127164131.2244124-6-daniel.vetter@ffwll.ch

diff --git a/drivers/media/common/videobuf2/videobuf2-memops.c b/drivers/media/common/videobuf2/videobuf2-memops.c
index 6e9e051..9dd6c27 100644 (file)
--- a/drivers/media/common/videobuf2/videobuf2-memops.c
+++ b/drivers/media/common/videobuf2/videobuf2-memops.c
@@ -40,7 +40,6 @@ struct frame_vector *vb2_create_framevec(unsigned long start,
        unsigned long first, last;
        unsigned long nr;
        struct frame_vector *vec;
-       unsigned int flags = FOLL_FORCE | FOLL_WRITE;
 
        first = start >> PAGE_SHIFT;
        last = (start + length - 1) >> PAGE_SHIFT;
@@ -48,7 +47,7 @@ struct frame_vector *vb2_create_framevec(unsigned long start,
        vec = frame_vector_create(nr);
        if (!vec)
                return ERR_PTR(-ENOMEM);
-       ret = get_vaddr_frames(start & PAGE_MASK, nr, flags, vec);
+       ret = get_vaddr_frames(start & PAGE_MASK, nr, vec);
        if (ret < 0)
                goto out_destroy;
        /* We accept only complete set of PFNs */

diff --git a/include/linux/mm.h b/include/linux/mm.h
index ecdf8a8..2e7b1d0 100644 (file)
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1768,7 +1768,7 @@ struct frame_vector {
 struct frame_vector *frame_vector_create(unsigned int nr_frames);
 void frame_vector_destroy(struct frame_vector *vec);
 int get_vaddr_frames(unsigned long start, unsigned int nr_pfns,
-                    unsigned int gup_flags, struct frame_vector *vec);
+                    struct frame_vector *vec);
 void put_vaddr_frames(struct frame_vector *vec);
 int frame_vector_to_pages(struct frame_vector *vec);
 void frame_vector_to_pfns(struct frame_vector *vec);

diff --git a/mm/frame_vector.c b/mm/frame_vector.c
index 10f82d5..f8c34b8 100644 (file)
--- a/mm/frame_vector.c
+++ b/mm/frame_vector.c
@@ -32,13 +32,12 @@
  * This function takes care of grabbing mmap_lock as necessary.
  */
 int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
-                    unsigned int gup_flags, struct frame_vector *vec)
+                    struct frame_vector *vec)
 {
        struct mm_struct *mm = current->mm;
        struct vm_area_struct *vma;
        int ret = 0;
        int err;
-       int locked;
 
        if (nr_frames == 0)
                return 0;
@@ -48,40 +47,26 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 
        start = untagged_addr(start);
 
-       mmap_read_lock(mm);
-       locked = 1;
-       vma = find_vma_intersection(mm, start, start + 1);
-       if (!vma) {
-               ret = -EFAULT;
-               goto out;
-       }
-
-       /*
-        * While get_vaddr_frames() could be used for transient (kernel
-        * controlled lifetime) pinning of memory pages all current
-        * users establish long term (userspace controlled lifetime)
-        * page pinning. Treat get_vaddr_frames() like
-        * get_user_pages_longterm() and disallow it for filesystem-dax
-        * mappings.
-        */
-       if (vma_is_fsdax(vma)) {
-               ret = -EOPNOTSUPP;
-               goto out;
-       }
-
-       if (!(vma->vm_flags & (VM_IO | VM_PFNMAP))) {
+       ret = pin_user_pages_fast(start, nr_frames,
+                                 FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM,
+                                 (struct page **)(vec->ptrs));
+       if (ret > 0) {
                vec->got_ref = true;
                vec->is_pfns = false;
-               ret = pin_user_pages_locked(start, nr_frames,
-                       gup_flags, (struct page **)(vec->ptrs), &locked);
-               goto out;
+               goto out_unlocked;
        }
 
+       mmap_read_lock(mm);
        vec->got_ref = false;
        vec->is_pfns = true;
+       ret = 0;
        do {
                unsigned long *nums = frame_vector_pfns(vec);
 
+               vma = find_vma_intersection(mm, start, start + 1);
+               if (!vma)
+                       break;
+
                while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
                        err = follow_pfn(vma, start, &nums[ret]);
                        if (err) {
@@ -92,17 +77,13 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
                        start += PAGE_SIZE;
                        ret++;
                }
-               /*
-                * We stop if we have enough pages or if VMA doesn't completely
-                * cover the tail page.
-                */
-               if (ret >= nr_frames || start < vma->vm_end)
+               /* Bail out if VMA doesn't completely cover the tail page. */
+               if (start < vma->vm_end)
                        break;
-               vma = find_vma_intersection(mm, start, start + 1);
-       } while (vma && vma->vm_flags & (VM_IO | VM_PFNMAP));
+       } while (ret < nr_frames);
 out:
-       if (locked)
-               mmap_read_unlock(mm);
+       mmap_read_unlock(mm);
+out_unlocked:
        if (!ret)
                ret = -EFAULT;
        if (ret > 0)