Commit 04769cb1 authored by Daniel Vetter's avatar Daniel Vetter
Browse files

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: default avatarDaniel 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: default avatarDaniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20201127164131.2244124-6-daniel.vetter@ffwll.ch
parent d88a0c16

drivers/media/common/videobuf2/videobuf2-memops.c

+1 −2
Original line number Diff line number Diff line
@@ -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 */

include/linux/mm.h

+1 −1
Original line number Diff line number Diff line
@@ -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);

mm/frame_vector.c

+17 −36
Original line number Diff line number Diff line
@@ -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);

out_unlocked:

	if (!ret)

		ret = -EFAULT;

	if (ret > 0)