mm-secretmem-fix-gup-fast-succeeding-on-secretmem-folios.patch removed from -mm tree

The quilt patch titled
Subject: mm/secretmem: fix GUP-fast succeeding on secretmem folios
has been removed from the -mm tree. Its filename was
mm-secretmem-fix-gup-fast-succeeding-on-secretmem-folios.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: David Hildenbrand <[email protected]>
Subject: mm/secretmem: fix GUP-fast succeeding on secretmem folios
Date: Tue, 26 Mar 2024 15:32:08 +0100

folio_is_secretmem() currently relies on secretmem folios being LRU folios, to save some cycles.

However, folios might reside in a folio batch without the LRU flag set, or temporarily have their LRU flag cleared. Consequently, the LRU flag is unreliable for this purpose.

In particular, this is the case when secretmem_fault() allocates a fresh page and calls filemap_add_folio()->folio_add_lru(). The folio might be added to the per-cpu folio batch and won't get the LRU flag set until the batch was drained using e.g., lru_add_drain().

Consequently, folio_is_secretmem() might not detect secretmem folios and GUP-fast can succeed in grabbing a secretmem folio, crashing the kernel when we would later try reading/writing to the folio, because the folio has been unmapped from the directmap.

Fix it by removing that unreliable check.

---

 include/linux/secretmem.h |    4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

@@ -13,10 +13,10 @@ static inline bool folio_is_secretmem(st
 	/*
 	 * Using folio_mapping() is quite slow because of the actual call
 	 * instruction.
-	 * We know that secretmem pages are not compound and LRU so we can
+	 * We know that secretmem pages are not compound, so we can
 	 * save a couple of cycles here.
 	 */
-	if (folio_test_large(folio) || !folio_test_lru(folio))
+	if (folio_test_large(folio))
 		return false;
 
 	mapping = (struct address_space *)

_

Patches currently in -mm which might be from [email protected] are

mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly.patch mm-madvise-dont-perform-madvise-vma-walk-for-madv_populate_readwrite.patch mm-userfaultfd-dont-place-zeropages-when-zeropages-are-disallowed.patch s390-mm-re-enable-the-shared-zeropage-for-pv-and-skeys-kvm-guests.patch mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared.patch mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared-fix.patch selftests-memfd_secret-add-vmsplice-test.patch mm-merge-folio_is_secretmem-and-folio_fast_pin_allowed-into-gup_fast_folio_allowed.patch mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch mm-remove-prot-parameter-from-move_pte.patch mm-gup-consistently-name-gup-fast-functions.patch mm-treewide-rename-config_have_fast_gup-to-config_have_gup_fast.patch mm-use-gup-fast-instead-fast-gup-in-remaining-comments.patch