+ mm-huge_memory-split-huge-pmd-under-one-pte_offset_map.patch added to mm-unstable branch

+ mm-huge_memory-split-huge-pmd-under-one-pte_offset_map.patch added to mm-unstable branch

[Andrew Morton]

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The patch titled
     Subject: mm/huge_memory: split huge pmd under one pte_offset_map()
has been added to the -mm mm-unstable branch.  Its filename is
     mm-huge_memory-split-huge-pmd-under-one-pte_offset_map.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-huge_memory-split-huge-pmd-under-one-pte_offset_map.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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------------------------------------------------------
From: Hugh Dickins <hughd@google.com>
Subject: mm/huge_memory: split huge pmd under one pte_offset_map()
Date: Thu, 8 Jun 2023 18:41:31 -0700 (PDT)

__split_huge_zero_page_pmd() use a single pte_offset_map() to sweep the
extent: it's already under pmd_lock(), so this is no worse for latency;
and since it's supposed to have full control of the just-withdrawn page
table, here choose to VM_BUG_ON if it were to fail.  And please don't
increment haddr by PAGE_SIZE, that should remain huge aligned: declare a
separate addr (not a bugfix, but it was deceptive).

__split_huge_pmd_locked() likewise (but it had declared a separate addr);
and change its BUG_ON(!pte_none) to VM_BUG_ON, for consistency with zero
(those deposited page tables are sometimes victims of random corruption).

Link: https://lkml.kernel.org/r/90cbed7f-90d9-b779-4a46-d2485baf9595@google.com
Signed-off-by: Hugh Dickins <hughd@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: 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: Yu Zhao <yuzhao@google.com>
Cc: Zack Rusin <zackr@vmware.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/huge_memory.c |   28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

--- a/mm/huge_memory.c~mm-huge_memory-split-huge-pmd-under-one-pte_offset_map
+++ a/mm/huge_memory.c
@@ -2037,6 +2037,8 @@ static void __split_huge_zero_page_pmd(s
 	struct mm_struct *mm = vma->vm_mm;
 	pgtable_t pgtable;
 	pmd_t _pmd, old_pmd;
+	unsigned long addr;
+	pte_t *pte;
 	int i;
 
 	/*
@@ -2052,17 +2054,20 @@ static void __split_huge_zero_page_pmd(s
 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
 	pmd_populate(mm, &_pmd, pgtable);
 
-	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
-		pte_t *pte, entry;
-		entry = pfn_pte(my_zero_pfn(haddr), vma->vm_page_prot);
+	pte = pte_offset_map(&_pmd, haddr);
+	VM_BUG_ON(!pte);
+	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
+		pte_t entry;
+
+		entry = pfn_pte(my_zero_pfn(addr), vma->vm_page_prot);
 		entry = pte_mkspecial(entry);
 		if (pmd_uffd_wp(old_pmd))
 			entry = pte_mkuffd_wp(entry);
-		pte = pte_offset_map(&_pmd, haddr);
 		VM_BUG_ON(!pte_none(*pte));
-		set_pte_at(mm, haddr, pte, entry);
-		pte_unmap(pte);
+		set_pte_at(mm, addr, pte, entry);
+		pte++;
 	}
+	pte_unmap(pte - 1);
 	smp_wmb(); /* make pte visible before pmd */
 	pmd_populate(mm, pmd, pgtable);
 }
@@ -2077,6 +2082,7 @@ static void __split_huge_pmd_locked(stru
 	bool young, write, soft_dirty, pmd_migration = false, uffd_wp = false;
 	bool anon_exclusive = false, dirty = false;
 	unsigned long addr;
+	pte_t *pte;
 	int i;
 
 	VM_BUG_ON(haddr & ~HPAGE_PMD_MASK);
@@ -2205,8 +2211,10 @@ static void __split_huge_pmd_locked(stru
 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
 	pmd_populate(mm, &_pmd, pgtable);
 
+	pte = pte_offset_map(&_pmd, haddr);
+	VM_BUG_ON(!pte);
 	for (i = 0, addr = haddr; i < HPAGE_PMD_NR; i++, addr += PAGE_SIZE) {
-		pte_t entry, *pte;
+		pte_t entry;
 		/*
 		 * Note that NUMA hinting access restrictions are not
 		 * transferred to avoid any possibility of altering
@@ -2249,11 +2257,11 @@ static void __split_huge_pmd_locked(stru
 				entry = pte_mkuffd_wp(entry);
 			page_add_anon_rmap(page + i, vma, addr, false);
 		}
-		pte = pte_offset_map(&_pmd, addr);
-		BUG_ON(!pte_none(*pte));
+		VM_BUG_ON(!pte_none(*pte));
 		set_pte_at(mm, addr, pte, entry);
-		pte_unmap(pte);
+		pte++;
 	}
+	pte_unmap(pte - 1);
 
 	if (!pmd_migration)
 		page_remove_rmap(page, vma, true);
_

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