+ mm-migrate_device-allow-pte_offset_map_lock-to-fail.patch added to mm-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

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The patch titled
     Subject: mm/migrate_device: allow pte_offset_map_lock() to fail
has been added to the -mm mm-unstable branch.  Its filename is
     mm-migrate_device-allow-pte_offset_map_lock-to-fail.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-migrate_device-allow-pte_offset_map_lock-to-fail.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/migrate_device: allow pte_offset_map_lock() to fail
Date: Thu, 8 Jun 2023 18:38:17 -0700 (PDT)

migrate_vma_collect_pmd(): remove the pmd_trans_unstable() handling after
splitting huge zero pmd, and the pmd_none() handling after successfully
splitting huge page: those are now managed inside pte_offset_map_lock(),
and by "goto again" when it fails.

But the skip after unsuccessful split_huge_page() must stay: it avoids an
endless loop.  The skip when pmd_bad()?  Remove that: it will be treated
as a hole rather than a skip once cleared by pte_offset_map_lock(), but
with different timing that would be so anyway; and it's arguably best to
leave the pmd_bad() handling centralized there.

migrate_vma_insert_page(): remove comment on the old pte_offset_map() and
old locking limitations; remove the pmd_trans_unstable() check and just
proceed to pte_offset_map_lock(), aborting when it fails (page has been
charged to memcg, but as in other cases, it's uncharged when freed).

Link: https://lkml.kernel.org/r/1131be62-2e84-da2f-8f45-807b2cbeeec5@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Alistair Popple <apopple@nvidia.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Christophe Leroy <christophe.leroy@csgroup.eu>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Lorenzo Stoakes <lstoakes@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Naoya Horiguchi <naoya.horiguchi@nec.com>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Qi Zheng <zhengqi.arch@bytedance.com>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <song@kernel.org>
Cc: Steven Price <steven.price@arm.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Will Deacon <will@kernel.org>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/migrate_device.c |   31 ++++---------------------------
 1 file changed, 4 insertions(+), 27 deletions(-)

--- a/mm/migrate_device.c~mm-migrate_device-allow-pte_offset_map_lock-to-fail
+++ a/mm/migrate_device.c
@@ -83,9 +83,6 @@ again:
 		if (is_huge_zero_page(page)) {
 			spin_unlock(ptl);
 			split_huge_pmd(vma, pmdp, addr);
-			if (pmd_trans_unstable(pmdp))
-				return migrate_vma_collect_skip(start, end,
-								walk);
 		} else {
 			int ret;
 
@@ -100,16 +97,12 @@ again:
 			if (ret)
 				return migrate_vma_collect_skip(start, end,
 								walk);
-			if (pmd_none(*pmdp))
-				return migrate_vma_collect_hole(start, end, -1,
-								walk);
 		}
 	}
 
-	if (unlikely(pmd_bad(*pmdp)))
-		return migrate_vma_collect_skip(start, end, walk);
-
 	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
+	if (!ptep)
+		goto again;
 	arch_enter_lazy_mmu_mode();
 
 	for (; addr < end; addr += PAGE_SIZE, ptep++) {
@@ -595,27 +588,10 @@ static void migrate_vma_insert_page(stru
 	pmdp = pmd_alloc(mm, pudp, addr);
 	if (!pmdp)
 		goto abort;
-
 	if (pmd_trans_huge(*pmdp) || pmd_devmap(*pmdp))
 		goto abort;
-
-	/*
-	 * Use pte_alloc() instead of pte_alloc_map().  We can't run
-	 * pte_offset_map() on pmds where a huge pmd might be created
-	 * from a different thread.
-	 *
-	 * pte_alloc_map() is safe to use under mmap_write_lock(mm) or when
-	 * parallel threads are excluded by other means.
-	 *
-	 * Here we only have mmap_read_lock(mm).
-	 */
 	if (pte_alloc(mm, pmdp))
 		goto abort;
-
-	/* See the comment in pte_alloc_one_map() */
-	if (unlikely(pmd_trans_unstable(pmdp)))
-		goto abort;
-
 	if (unlikely(anon_vma_prepare(vma)))
 		goto abort;
 	if (mem_cgroup_charge(page_folio(page), vma->vm_mm, GFP_KERNEL))
@@ -650,7 +626,8 @@ static void migrate_vma_insert_page(stru
 	}
 
 	ptep = pte_offset_map_lock(mm, pmdp, addr, &ptl);
-
+	if (!ptep)
+		goto abort;
 	if (check_stable_address_space(mm))
 		goto unlock_abort;
 
_

Patches currently in -mm which might be from hughd@google.com are

arm-allow-pte_offset_map-to-fail.patch
arm64-allow-pte_offset_map-to-fail.patch
arm64-hugetlb-pte_alloc_huge-pte_offset_huge.patch
ia64-hugetlb-pte_alloc_huge-pte_offset_huge.patch
m68k-allow-pte_offset_map-to-fail.patch
microblaze-allow-pte_offset_map-to-fail.patch
mips-update_mmu_cache-can-replace-__update_tlb.patch
mips-update_mmu_cache-can-replace-__update_tlb-fix.patch
parisc-add-pte_unmap-to-balance-get_ptep.patch
parisc-unmap_uncached_pte-use-pte_offset_kernel.patch
parisc-hugetlb-pte_alloc_huge-pte_offset_huge.patch
powerpc-kvmppc_unmap_free_pmd-pte_offset_kernel.patch
powerpc-allow-pte_offset_map-to-fail.patch
powerpc-hugetlb-pte_alloc_huge.patch
riscv-hugetlb-pte_alloc_huge-pte_offset_huge.patch
s390-allow-pte_offset_map_lock-to-fail.patch
s390-gmap-use-pte_unmap_unlock-not-spin_unlock.patch
sh-hugetlb-pte_alloc_huge-pte_offset_huge.patch
sparc-hugetlb-pte_alloc_huge-pte_offset_huge.patch
sparc-allow-pte_offset_map-to-fail.patch
sparc-iounit-and-iommu-use-pte_offset_kernel.patch
x86-allow-get_locked_pte-to-fail.patch
x86-sme_populate_pgd-use-pte_offset_kernel.patch
xtensa-add-pte_unmap-to-balance-pte_offset_map.patch
mm-use-pmdp_get_lockless-without-surplus-barrier.patch
mm-migrate-remove-cruft-from-migration_entry_waits.patch
mm-pgtable-kmap_local_page-instead-of-kmap_atomic.patch
mm-pgtable-allow-pte_offset_map-to-fail.patch
mm-filemap-allow-pte_offset_map_lock-to-fail.patch
mm-page_vma_mapped-delete-bogosity-in-page_vma_mapped_walk.patch
mm-page_vma_mapped-reformat-map_pte-with-less-indentation.patch
mm-page_vma_mapped-pte_offset_map_nolock-not-pte_lockptr.patch
mm-pagewalkers-action_again-if-pte_offset_map_lock-fails.patch
mm-pagewalk-walk_pte_range-allow-for-pte_offset_map.patch
mm-vmwgfx-simplify-pmd-pud-mapping-dirty-helpers.patch
mm-vmalloc-vmalloc_to_page-use-pte_offset_kernel.patch
mm-hmm-retry-if-pte_offset_map-fails.patch
mm-userfaultfd-retry-if-pte_offset_map-fails.patch
mm-userfaultfd-allow-pte_offset_map_lock-to-fail.patch
mm-debug_vm_pgtablepage_table_check-warn-pte-map-fails.patch
mm-various-give-up-if-pte_offset_map-fails.patch
mm-mprotect-delete-pmd_none_or_clear_bad_unless_trans_huge.patch
mm-mremap-retry-if-either-pte_offset_map_lock-fails.patch
mm-madvise-clean-up-pte_offset_map_lock-scans.patch
mm-madvise-clean-up-force_shm_swapin_readahead.patch
mm-swapoff-allow-pte_offset_map-to-fail.patch
mm-mglru-allow-pte_offset_map_nolock-to-fail.patch
mm-migrate_device-allow-pte_offset_map_lock-to-fail.patch
mm-gup-remove-foll_split_pmd-use-of-pmd_trans_unstable.patch
mm-huge_memory-split-huge-pmd-under-one-pte_offset_map.patch
mm-khugepaged-allow-pte_offset_map-to-fail.patch
mm-memory-allow-pte_offset_map-to-fail.patch
mm-memory-handle_pte_fault-use-pte_offset_map_nolock.patch
mm-pgtable-delete-pmd_trans_unstable-and-friends.patch
mm-swap-swap_vma_readahead-do-the-pte_offset_map.patch
perf-core-allow-pte_offset_map-to-fail.patch