Merge tag 'random-6.11-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random

Pull random number generator updates from Jason Donenfeld:
 "This adds getrandom() support to the vDSO.

  First, it adds a new kind of mapping to mmap(2), MAP_DROPPABLE, which
  lets the kernel zero out pages anytime under memory pressure, which
  enables allocating memory that never gets swapped to disk but also
  doesn't count as being mlocked.

  Then, the vDSO implementation of getrandom() is introduced in a
  generic manner and hooked into random.c.

  Next, this is implemented on x86. (Also, though it's not ready for
  this pull, somebody has begun an arm64 implementation already)

  Finally, two vDSO selftests are added.

  There are also two housekeeping cleanup commits"

* tag 'random-6.11-rc1-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/crng/random:
  MAINTAINERS: add random.h headers to RNG subsection
  random: note that RNDGETPOOL was removed in 2.6.9-rc2
  selftests/vDSO: add tests for vgetrandom
  x86: vdso: Wire up getrandom() vDSO implementation
  random: introduce generic vDSO getrandom() implementation
  mm: add MAP_DROPPABLE for designating always lazily freeable mappings

1 files changed, 18 insertions, 3 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 8616308610b9..2490e727e2dc 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1412,7 +1412,11 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
 	VM_BUG_ON_VMA(address < vma->vm_start ||
 			address + (nr << PAGE_SHIFT) > vma->vm_end, vma);
 
-	if (!folio_test_swapbacked(folio))
+	/*
+	 * VM_DROPPABLE mappings don't swap; instead they're just dropped when
+	 * under memory pressure.
+	 */
+	if (!folio_test_swapbacked(folio) && !(vma->vm_flags & VM_DROPPABLE))
 		__folio_set_swapbacked(folio);
 	__folio_set_anon(folio, vma, address, exclusive);
 
@@ -1848,7 +1852,13 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				 * plus the rmap(s) (dropped by discard:).
 				 */
 				if (ref_count == 1 + map_count &&
-				    !folio_test_dirty(folio)) {
+				    (!folio_test_dirty(folio) ||
+				     /*
+				      * Unlike MADV_FREE mappings, VM_DROPPABLE
+				      * ones can be dropped even if they've
+				      * been dirtied.
+				      */
+				     (vma->vm_flags & VM_DROPPABLE))) {
 					dec_mm_counter(mm, MM_ANONPAGES);
 					goto discard;
 				}
@@ -1858,7 +1868,12 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
 				 * discarded. Remap the page to page table.
 				 */
 				set_pte_at(mm, address, pvmw.pte, pteval);
-				folio_set_swapbacked(folio);
+				/*
+				 * Unlike MADV_FREE mappings, VM_DROPPABLE ones
+				 * never get swap backed on failure to drop.
+				 */
+				if (!(vma->vm_flags & VM_DROPPABLE))
+					folio_set_swapbacked(folio);
 				goto walk_abort;
 			}