[merged mm-hotfixes-stable] fix-incorrect-flush-address-in-direct-page-table-reclaim.patch removed from -mm tree

The quilt patch titled
     Subject: mm: fix incorrect flush address in direct page table reclaim
has been removed from the -mm tree.  Its filename was
     fix-incorrect-flush-address-in-direct-page-table-reclaim.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: Andy Lutomirski <[email protected]>
Subject: mm: fix incorrect flush address in direct page table reclaim
Date: Mon, 3 Aug 2026 17:37:08 -0700

When zap_pte_range reclaims a page table, it does:

    pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);

and this is unconditionally wrong: if this code executes, addr *always*
points one past the end of the range covered by the table.  The addr
parameter is used to flush the TLB (really the paging-structure-cache) to
drop references to the to-be-freed table, and any architecture that cares
about the parameter will flush the wrong address.  (But they'll still free
the correct page).

I think it's worth contemplating why the kernel works at all.

If we hit the offending line of code, we will first clear the PMD entry
(line 1954, zap_empty_pte_table), then we will issue pending flushes if
force_flush is set (tlb_flush_mmu_tlbonly(tlb)), then we will skip the
retry on line 1979 (phew!), and then we will do the offending pte_free_tlb
call.  *Or* we will clear the PMD entry immediately before pte_free_tlb
(line 1983, zap_pte_table_if_empty).

If we have any pending flushes (i.e.  we actually zapped any last-level
entries) at the time we clear the PMD entry, then the flush really ought
to flush all references to the table (Linus certainly seems to think it
will on all architectures [0]).

The condition under which we have no accumulated flushes at the time of
the clear is very complex (the whole zap_pte_range function has absurdly
complex control flow).  If we do hit the bad case, then we will end up
clearing the PMD entry after the last time the range is flushed, and any
CPU is free to cache a reference to the (empty) page table.  If this
happens due to an ordinary read or write, it would segfault, so it would
be rare.  But the cache could be speculatively filled as well.  Then we'll
flush the wrong address and then free and possibly reuse the table.

On x86, even flushing the wrong address works on non-KPTI Intel systems
because INVLPG flushes *all* paging-structure-caches, not just the ones
for the target address.  But INVPCID does not, and flush_tlb_one_user will
use INVPCID if it's available.  And then we're toast.  AMD systems are
more susceptible: we set the EFER.TCE bit, which makes even INVLPG only
flush the target address.

I think this might fix an issue in ripgrep reported here [1]:

Link: https://lore.kernel.org/[email protected]
Link: https://lore.kernel.org/all/CA+55aFzBggoXtNXQeng5d_mRoDnaMBE5Y+URs+PHR67nUpMtaw@mail.gmail.com/T/#u [0]
Link: https://github.com/BurntSushi/ripgrep/issues/3494 [1]
Link: https://github.com/dfoxfranke/ripgrep-3494-analysis
Fixes: 4c640eb4181c ("mm: move pte table reclaim code to memory.c")
Signed-off-by: Andy Lutomirski <[email protected]>
Acked-by: David Hildenbrand (Arm) <[email protected]>
Acked-by: Qi Zheng <[email protected]>
Acked-by: Vlastimil Babka (SUSE) <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: Liam Howlett <[email protected]>
Cc: Lorenzo Stoakes <[email protected]>
Cc: Mike Rapoport <[email protected]>
Cc: Suren Baghdasaryan <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
---

 mm/memory.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/memory.c~fix-incorrect-flush-address-in-direct-page-table-reclaim
+++ a/mm/memory.c
@@ -1981,7 +1981,7 @@ retry:
 
 	if (can_reclaim_pt) {
 		if (direct_reclaim || zap_pte_table_if_empty(mm, pmd, start, &pmdval)) {
-			pte_free_tlb(tlb, pmd_pgtable(pmdval), addr);
+			pte_free_tlb(tlb, pmd_pgtable(pmdval), start);
 			mm_dec_nr_ptes(mm);
 		}
 	}
_

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