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Re: [PATCH v2 2/3] xen/privcmd: Mark pages as dirty

On 07.07.20 13:30, Souptick Joarder wrote:
On Tue, Jul 7, 2020 at 3:08 PM Jürgen Groß <jgross@xxxxxxxx> wrote:

On 06.07.20 20:16, Souptick Joarder wrote:
pages need to be marked as dirty before unpinned it in
unlock_pages() which was oversight. This is fixed now.

Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
Suggested-by: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
Cc: Paul Durrant <xadimgnik@xxxxxxxxx>
   drivers/xen/privcmd.c | 5 ++++-
   1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/xen/privcmd.c b/drivers/xen/privcmd.c
index 33677ea..f6c1543 100644
--- a/drivers/xen/privcmd.c
+++ b/drivers/xen/privcmd.c
@@ -612,8 +612,11 @@ static void unlock_pages(struct page *pages[], unsigned 
int nr_pages)
       unsigned int i;

-     for (i = 0; i < nr_pages; i++)
+     for (i = 0; i < nr_pages; i++) {
+             if (!PageDirty(pages[i]))
+                     set_page_dirty_lock(pages[i]);

With put_page() directly following I think you should be able to use
set_page_dirty() instead, as there is obviously a reference to the page

Patch [3/3] will convert above codes to use unpin_user_pages_dirty_lock()
which internally do the same check. So I thought to keep linux-stable and
linux-next code in sync. John had a similar concern [1] and later agreed to keep
this check.

Shall I keep this check ?  No ?


I wasn't referring to checking PageDirty(), but to the use of

Looking at the comment just before the implementation of
set_page_dirty_lock() suggests that it is fine to use set_page_dirty()
instead (so not calling lock_page()).

Only the transition from get_user_pages_fast() to pin_user_pages_fast()
requires to use the locked version IMO.




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