[merged mm-hotfixes-stable] mm-migrate_devicec-flush-tlb-while-holding-ptl.patch removed from -mm tree

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The quilt patch titled
     Subject: mm/migrate_device.c: flush TLB while holding PTL
has been removed from the -mm tree.  Its filename was
     mm-migrate_devicec-flush-tlb-while-holding-ptl.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: Alistair Popple <apopple@xxxxxxxxxx>
Subject: mm/migrate_device.c: flush TLB while holding PTL
Date: Fri, 2 Sep 2022 10:35:51 +1000

When clearing a PTE the TLB should be flushed whilst still holding the PTL
to avoid a potential race with madvise/munmap/etc.  For example consider
the following sequence:

  CPU0                          CPU1
  ----                          ----

  migrate_vma_collect_pmd()
  pte_unmap_unlock()
                                madvise(MADV_DONTNEED)
                                -> zap_pte_range()
                                pte_offset_map_lock()
                                [ PTE not present, TLB not flushed ]
                                pte_unmap_unlock()
                                [ page is still accessible via stale TLB ]
  flush_tlb_range()

In this case the page may still be accessed via the stale TLB entry after
madvise returns.  Fix this by flushing the TLB while holding the PTL.

Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Link: https://lkml.kernel.org/r/9f801e9d8d830408f2ca27821f606e09aa856899.1662078528.git-series.apopple@xxxxxxxxxx
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
Reported-by: Nadav Amit <nadav.amit@xxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Acked-by: David Hildenbrand <david@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Cc: Alex Sierra <alex.sierra@xxxxxxx>
Cc: Ben Skeggs <bskeggs@xxxxxxxxxx>
Cc: Felix Kuehling <Felix.Kuehling@xxxxxxx>
Cc: huang ying <huang.ying.caritas@xxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Karol Herbst <kherbst@xxxxxxxxxx>
Cc: Logan Gunthorpe <logang@xxxxxxxxxxxx>
Cc: Lyude Paul <lyude@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 mm/migrate_device.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/mm/migrate_device.c~mm-migrate_devicec-flush-tlb-while-holding-ptl
+++ a/mm/migrate_device.c
@@ -254,13 +254,14 @@ next:
 		migrate->dst[migrate->npages] = 0;
 		migrate->src[migrate->npages++] = mpfn;
 	}
-	arch_leave_lazy_mmu_mode();
-	pte_unmap_unlock(ptep - 1, ptl);
 
 	/* Only flush the TLB if we actually modified any entries */
 	if (unmapped)
 		flush_tlb_range(walk->vma, start, end);
 
+	arch_leave_lazy_mmu_mode();
+	pte_unmap_unlock(ptep - 1, ptl);
+
 	return 0;
 }
 
_

Patches currently in -mm which might be from apopple@xxxxxxxxxx are

mm-gupc-simplify-and-fix-check_and_migrate_movable_pages-return-codes.patch
selftests-hmm-tests-add-test-for-dirty-bits.patch
mm-gupc-dont-pass-gup_flags-to-check_and_migrate_movable_pages.patch
mm-gupc-refactor-check_and_migrate_movable_pages.patch
mm-migrate_devicec-fix-a-misleading-and-out-dated-comment.patch




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