Re: [PATCH v5 02/14] mm/gup: check every subpage of a compound page during isolation
From: Jason Gunthorpe <jgg@ziepe.ca>
Date: 2021-01-19 18:57:43
Also in:
linux-kselftest, linux-mm, lkml
On Mon, Jan 18, 2021 at 11:39:08PM -0500, Pavel Tatashin wrote:
When pages are isolated in check_and_migrate_movable_pages() we skip
compound number of pages at a time. However, as Jason noted, it is
not necessary correct that pages[i] corresponds to the pages that
we skipped. This is because it is possible that the addresses in
this range had split_huge_pmd()/split_huge_pud(), and these functions
do not update the compound page metadata.
The problem can be reproduced if something like this occurs:
1. User faulted huge pages.
2. split_huge_pmd() was called for some reason
3. User has unmapped some sub-pages in the range
4. User tries to longterm pin the addresses.
The resulting pages[i] might end-up having pages which are not compound
size page aligned.
Fixes: aa712399c1e8 ("mm/gup: speed up check_and_migrate_cma_pages() on huge page")
Reported-by: Jason Gunthorpe <jgg@nvidia.com>No new line after fixes
Signed-off-by: Pavel Tatashin <pasha.tatashin@soleen.com> mm/gup.c | 19 +++++++------------ 1 file changed, 7 insertions(+), 12 deletions(-)
Looks good Reviewed-by: Jason Gunthorpe <jgg@nvidia.com> Thanks, Jason