Re: [PATCH v5 08/14] mm/gup: do not allow zero page for pinned pages
From: Jason Gunthorpe <jgg@ziepe.ca>
Date: 2021-01-19 21:17:42
Also in:
linux-kselftest, linux-mm, lkml
On Tue, Jan 19, 2021 at 01:34:26PM -0500, Pavel Tatashin wrote:
On Tue, Jan 19, 2021 at 1:30 PM Jason Gunthorpe [off-list ref] wrote:quoted
On Mon, Jan 18, 2021 at 11:39:14PM -0500, Pavel Tatashin wrote:quoted
Zero page should not be used for long term pinned pages. Once pages are pinned their physical addresses cannot changed until they are unpinned. Guarantee to always return real pages when they are pinned by adding FOLL_WRITE. Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> mm/gup.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)No, this will definitely break thingsWhat will break
Things assuming GUP doesn't break COW, making all GUP WRITE was already tried and revered for some other reason
quoted
Why does the zero page have to be movable?It is not even about being movable, we can't cow pinned pages returned by GUP call, how can we use zero page for that?
The zero page is always zero, it is never written to. What does cow matter? Jason