[v2,2/2] vhost: convert get_user_pages() --> pin_user_pages()
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Message ID 20200601052633.853874-3-jhubbard@nvidia.com
State New
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Series
  • vhost, docs: convert to pin_user_pages(), new "case 5"
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Commit Message

John Hubbard June 1, 2020, 5:26 a.m. UTC
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/

Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: kvm@vger.kernel.org
Cc: virtualization@lists.linux-foundation.org
Cc: netdev@vger.kernel.org
Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/vhost/vhost.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

Comments

Pankaj Gupta June 2, 2020, 6:08 a.m. UTC | #1
> 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/
>
> Cc: Michael S. Tsirkin <mst@redhat.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: kvm@vger.kernel.org
> Cc: virtualization@lists.linux-foundation.org
> Cc: netdev@vger.kernel.org
> Signed-off-by: John Hubbard <jhubbard@nvidia.com>
> ---
>  drivers/vhost/vhost.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 21a59b598ed8..596132a96cd5 100644
> --- 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;
>  }

Acked-by: Pankaj Gupta <pankaj.gupta.linux@gmail.com>

Patch
diff mbox series

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 21a59b598ed8..596132a96cd5 100644
--- 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;
 }