The patch titled
Subject: mm/filemap: fix filemap_get_folios_contig THP panic
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-filemap-fix-filemap_get_folios_contig-thp-panic.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-filemap-fix-filemap_get_folios_contig-thp-panic.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Steve Sistare <steven.sistare@xxxxxxxxxx>
Subject: mm/filemap: fix filemap_get_folios_contig THP panic
Date: Tue, 3 Sep 2024 07:25:17 -0700
Patch series "memfd-pin huge page fixes".
Fix multiple bugs that occur when using memfd_pin_folios with hugetlb
pages and THP. The hugetlb bugs only bite when the page is not yet
faulted in when memfd_pin_folios is called. The THP bug bites when the
starting offset passed to memfd_pin_folios is not huge page aligned. See
the commit messages for details.
This patch (of 5):
memfd_pin_folios on memory backed by THP panics if the requested start
offset is not huge page aligned:
BUG: kernel NULL pointer dereference, address: 0000000000000036
RIP: 0010:filemap_get_folios_contig+0xdf/0x290
RSP: 0018:ffffc9002092fbe8 EFLAGS: 00010202
RAX: 0000000000000002 RBX: 0000000000000002 RCX: 0000000000000002
The fault occurs here, because xas_load returns a folio with value 2:
filemap_get_folios_contig()
for (folio = xas_load(&xas); folio && xas.xa_index <= end;
folio = xas_next(&xas)) {
...
if (!folio_try_get(folio)) <-- BOOM
"2" is an xarray sibling entry. We get it because memfd_pin_folios does
not round the indices passed to filemap_get_folios_contig to huge page
boundaries for THP, so we load from the middle of a huge page range see a
sibling. (It does round for hugetlbfs, at the is_file_hugepages test).
To fix, if the folio is a sibling, then return the next index as the
starting point for the next call to filemap_get_folios_contig.
Link: https://lkml.kernel.org/r/1725373521-451395-1-git-send-email-steven.sistare@xxxxxxxxxx
Link: https://lkml.kernel.org/r/1725373521-451395-2-git-send-email-steven.sistare@xxxxxxxxxx
Fixes: 89c1905d9c14 ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios")
Signed-off-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Peter Xu <peterx@xxxxxxxxxx>
Cc: Vivek Kasireddy <vivek.kasireddy@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 4 ++++
1 file changed, 4 insertions(+)
--- a/mm/filemap.c~mm-filemap-fix-filemap_get_folios_contig-thp-panic
+++ a/mm/filemap.c
@@ -2181,6 +2181,10 @@ unsigned filemap_get_folios_contig(struc
if (xa_is_value(folio))
goto update_start;
+ /* If we landed in the middle of a THP, continue at its end. */
+ if (xa_is_sibling(folio))
+ goto update_start;
+
if (!folio_try_get(folio))
goto retry;
_
Patches currently in -mm which might be from steven.sistare@xxxxxxxxxx are
mm-filemap-fix-filemap_get_folios_contig-thp-panic.patch
mm-hugetlb-fix-memfd_pin_folios-free_huge_pages-leak.patch
mm-hugetlb-fix-memfd_pin_folios-resv_huge_pages-leak.patch
mm-gup-fix-memfd_pin_folios-hugetlb-page-allocation.patch
mm-gup-fix-memfd_pin_folios-alloc-race-panic.patch
