vhost: convert get_user_pages() --> pin_user_pages()

This code was using get_user_pages*(), in approximately a "Case 5"
scenario (accessing the data within a page), 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>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jérôme Glisse <jglisse@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Link: http://lkml.kernel.org/r/20200529234309.484480-3-jhubbard@nvidia.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 21a59b5..596132a 100644 (file)
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -1762,15 +1762,14 @@ static int set_bit_to_user(int nr, void __user *addr)
        int bit = nr + (log % PAGE_SIZE) * 8;
        int r;
 
-       r = get_user_pages_fast(log, 1, FOLL_WRITE, &page);
+       r = pin_user_pages_fast(log, 1, FOLL_WRITE, &page);
        if (r < 0)
                return r;
        BUG_ON(r != 1);
        base = kmap_atomic(page);
        set_bit(bit, base);
        kunmap_atomic(base);
-       set_page_dirty_lock(page);
-       put_page(page);
+       unpin_user_pages_dirty_lock(&page, 1, true);
        return 0;
 }