This is based on Linux 5.7, plus one prerequisite patch:
"mm/gup: update pin_user_pages.rst for "case 3" (mmu notifiers)" [1]
Changes since v1: removed references to set_page_dirty*(), in response to
Souptick Joarder's review (thanks!).
Cover letter for v1, edited/updated slightly:
It recently became clear to me that there are some get_user_pages*()
callers that don't fit neatly into any of the four cases that are so
far listed in pin_user_pages.rst. vhost.c is one of those.
Add a Case 5 to the documentation, and refer to that when converting
vhost.c.
Thanks to Jan Kara for helping me (again) in understanding the
interaction between get_user_pages() and page writeback [2].
Note that I have only compile-tested the vhost.c patch, although that
does also include cross-compiling for a few other arches. Any run-time
testing would be greatly appreciated.
[1] https://lore.kernel.org/r/[email protected]
[2] https://lore.kernel.org/r/[email protected]
John Hubbard (2):
docs: mm/gup: pin_user_pages.rst: add a "case 5"
vhost: convert get_user_pages() --> pin_user_pages()
Documentation/core-api/pin_user_pages.rst | 18 ++++++++++++++++++
drivers/vhost/vhost.c | 5 ++---
2 files changed, 20 insertions(+), 3 deletions(-)
base-commit: 3d77e6a8804abcc0504c904bd6e5cdf3a5cf8162
--
2.26.2
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 <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: [email protected]
Cc: [email protected]
Cc: [email protected]
Signed-off-by: John Hubbard <[email protected]>
---
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;
}
--
2.26.2
> 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 <[email protected]>
> Cc: Jason Wang <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> Signed-off-by: John Hubbard <[email protected]>
> ---
> 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 <[email protected]>