The patch titled
Subject: mm/migrate_device.c: copy pte dirty bit to page
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Alistair Popple <apopple@xxxxxxxxxx>
Subject: mm/migrate_device.c: copy pte dirty bit to page
Date: Fri, 2 Sep 2022 10:35:53 +1000
migrate_vma_setup() has a fast path in migrate_vma_collect_pmd() that
installs migration entries directly if it can lock the migrating page.
When removing a dirty pte the dirty bit is supposed to be carried over to
the underlying page to prevent it being lost.
Currently migrate_vma_*() can only be used for private anonymous mappings.
That means loss of the dirty bit usually doesn't result in data loss
because these pages are typically not file-backed. However pages may be
backed by swap storage which can result in data loss if an attempt is made
to migrate a dirty page that doesn't yet have the PageDirty flag set.
In this case migration will fail due to unexpected references but the
dirty pte bit will be lost. If the page is subsequently reclaimed data
won't be written back to swap storage as it is considered uptodate,
resulting in data loss if the page is subsequently accessed.
Prevent this by copying the dirty bit to the page when removing the pte to
match what try_to_migrate_one() does.
Link: https://lkml.kernel.org/r/dd48e4882ce859c295c1a77612f66d198b0403f9.1662078528.git-series.apopple@xxxxxxxxxx
Fixes: 8c3328f1f36a ("mm/migrate: migrate_vma() unmap page from vma while collecting pages")
Signed-off-by: Alistair Popple <apopple@xxxxxxxxxx>
Acked-by: Peter Xu <peterx@xxxxxxxxxx>
Reviewed-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Reported-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
Acked-by: David Hildenbrand <david@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: Nadav Amit <nadav.amit@xxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxxx>
Cc: Ralph Campbell <rcampbell@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate_device.c | 9 +++++++--
1 file changed, 7 insertions(+), 2 deletions(-)
--- a/mm/migrate_device.c~mm-migrate_devicec-copy-pte-dirty-bit-to-page
+++ a/mm/migrate_device.c
@@ -7,6 +7,7 @@
#include <linux/export.h>
#include <linux/memremap.h>
#include <linux/migrate.h>
+#include <linux/mm.h>
#include <linux/mm_inline.h>
#include <linux/mmu_notifier.h>
#include <linux/oom.h>
@@ -196,7 +197,7 @@ again:
flush_cache_page(vma, addr, pte_pfn(*ptep));
anon_exclusive = PageAnon(page) && PageAnonExclusive(page);
if (anon_exclusive) {
- ptep_clear_flush(vma, addr, ptep);
+ pte = ptep_clear_flush(vma, addr, ptep);
if (page_try_share_anon_rmap(page)) {
set_pte_at(mm, addr, ptep, pte);
@@ -206,11 +207,15 @@ again:
goto next;
}
} else {
- ptep_get_and_clear(mm, addr, ptep);
+ pte = ptep_get_and_clear(mm, addr, ptep);
}
migrate->cpages++;
+ /* Set the dirty flag on the folio now the pte is gone. */
+ if (pte_dirty(pte))
+ folio_mark_dirty(page_folio(page));
+
/* Setup special migration page table entry */
if (mpfn & MIGRATE_PFN_WRITE)
entry = make_writable_migration_entry(
_
Patches currently in -mm which might be from apopple@xxxxxxxxxx are
mm-migrate_devicec-flush-tlb-while-holding-ptl.patch
mm-migrate_devicec-add-missing-flush_cache_page.patch
mm-migrate_devicec-copy-pte-dirty-bit-to-page.patch
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
