[22/54] vhost: convert get_user_pages() --> pin_user_pages()

Commit Message

Andrew Morton June 8, 2020, 4:41 a.m. UTC

From: John Hubbard <[e-mail]>
Subject: 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/

Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: John Hubbard <[e-mail]>
Reviewed-by: Jan Kara <[e-mail]>
Acked-by: Michael S. Tsirkin <[e-mail]>
Acked-by: Pankaj Gupta <[e-mail]>
Cc: Jason Wang <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Jérôme Glisse <[e-mail]>
Cc: Jonathan Corbet <[e-mail]>
Cc: Souptick Joarder <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 drivers/vhost/vhost.c |    5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Patch

--- a/drivers/vhost/vhost.c~vhost-convert-get_user_pages-pin_user_pages
+++ a/drivers/vhost/vhost.c
@@ -1762,15 +1762,14 @@  static int set_bit_to_user(int nr, void
 	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;
 }