Commit 6647e76ab623 for kernel

commit 6647e76ab623b2b3fb2efe03a86e9c9046c52c33
Author: Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed Nov 30 16:10:52 2022 -0800

    v4l2: don't fall back to follow_pfn() if pin_user_pages_fast() fails

    The V4L2_MEMORY_USERPTR interface is long deprecated and shouldn't be
    used (and is discouraged for any modern v4l drivers).  And Seth Jenkins
    points out that the fallback to VM_PFNMAP/VM_IO is fundamentally racy
    and dangerous.

    Note that it's not even a case that should trigger, since any normal
    user pointer logic ends up just using the pin_user_pages_fast() call
    that does the proper page reference counting.  That's not the problem
    case, only if you try to use special device mappings do you have any
    issues.

    Normally I'd just remove this during the merge window, but since Seth
    pointed out the problem cases, we really want to know as soon as
    possible if there are actually any users of this odd special case of a
    legacy interface.  Neither Hans nor Mauro seem to think that such
    mis-uses of the old legacy interface should exist.  As Mauro says:

     "See, V4L2 has actually 4 streaming APIs:
            - Kernel-allocated mmap (usually referred simply as just mmap);
            - USERPTR mmap;
            - read();
            - dmabuf;

      The USERPTR is one of the oldest way to use it, coming from V4L
      version 1 times, and by far the least used one"

    And Hans chimed in on the USERPTR interface:

     "To be honest, I wouldn't mind if it goes away completely, but that's a
      bit of a pipe dream right now"

    but while removing this legacy interface entirely may be a pipe dream we
    can at least try to remove the unlikely (and actively broken) case of
    using special device mappings for USERPTR accesses.

    This replaces it with a WARN_ONCE() that we can remove once we've
    hopefully confirmed that no actual users exist.

    NOTE! Longer term, this means that a 'struct frame_vector' only ever
    contains proper page pointers, and all the games we have with converting
    them to pages can go away (grep for 'frame_vector_to_pages()' and the
    uses of 'vec->is_pfns').  But this is just the first step, to verify
    that this code really is all dead, and do so as quickly as possible.

    Reported-by: Seth Jenkins <sethjenkins@google.com>
    Acked-by: Hans Verkuil <hverkuil@xs4all.nl>
    Acked-by: Mauro Carvalho Chehab <mchehab@kernel.org>
    Cc: David Hildenbrand <david@redhat.com>
    Cc: Jan Kara <jack@suse.cz>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/media/common/videobuf2/frame_vector.c b/drivers/media/common/videobuf2/frame_vector.c
index 542dde9d2609..144027035892 100644
--- a/drivers/media/common/videobuf2/frame_vector.c
+++ b/drivers/media/common/videobuf2/frame_vector.c
@@ -35,11 +35,7 @@
 int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 		     struct frame_vector *vec)
 {
-	struct mm_struct *mm = current->mm;
-	struct vm_area_struct *vma;
-	int ret_pin_user_pages_fast = 0;
-	int ret = 0;
-	int err;
+	int ret;

 	if (nr_frames == 0)
 		return 0;
@@ -52,57 +48,17 @@ int get_vaddr_frames(unsigned long start, unsigned int nr_frames,
 	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;
-		goto out_unlocked;
-	}
-	ret_pin_user_pages_fast = ret;
-
-	mmap_read_lock(mm);
-	vec->got_ref = false;
-	vec->is_pfns = true;
-	ret = 0;
-	do {
-		unsigned long *nums = frame_vector_pfns(vec);
-
-		vma = vma_lookup(mm, start);
-		if (!vma)
-			break;
-
-		while (ret < nr_frames && start + PAGE_SIZE <= vma->vm_end) {
-			err = follow_pfn(vma, start, &nums[ret]);
-			if (err) {
-				if (ret)
-					goto out;
-				// If follow_pfn() returns -EINVAL, then this
-				// is not an IO mapping or a raw PFN mapping.
-				// In that case, return the original error from
-				// pin_user_pages_fast(). Otherwise this
-				// function would return -EINVAL when
-				// pin_user_pages_fast() returned -ENOMEM,
-				// which makes debugging hard.
-				if (err == -EINVAL && ret_pin_user_pages_fast)
-					ret = ret_pin_user_pages_fast;
-				else
-					ret = err;
-				goto out;
-			}
-			start += PAGE_SIZE;
-			ret++;
-		}
-		/* Bail out if VMA doesn't completely cover the tail page. */
-		if (start < vma->vm_end)
-			break;
-	} while (ret < nr_frames);
-out:
-	mmap_read_unlock(mm);
-out_unlocked:
-	if (!ret)
-		ret = -EFAULT;
-	if (ret > 0)
-		vec->nr_frames = ret;
-	return ret;
+	vec->got_ref = true;
+	vec->is_pfns = false;
+	vec->nr_frames = ret;
+
+	if (likely(ret > 0))
+		return ret;
+
+	/* This used to (racily) return non-refcounted pfns. Let people know */
+	WARN_ONCE(1, "get_vaddr_frames() cannot follow VM_IO mapping");
+	vec->nr_frames = 0;
+	return ret ? ret : -EFAULT;
 }
 EXPORT_SYMBOL(get_vaddr_frames);