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c225c4f605
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@oracle.com
Link: https://lkml.kernel.org/r/1725373521-451395-2-git-send-email-steven.sistare@oracle.com
Fixes: 89c1905d9c ("mm/gup: introduce memfd_pin_folios() for pinning memfd folios")
Signed-off-by: Steve Sistare <steven.sistare@oracle.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Peter Xu <peterx@redhat.com>
Cc: Vivek Kasireddy <vivek.kasireddy@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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