The quilt patch titled Subject: mm/madvise: make MADV_POPULATE_(READ|WRITE) handle VM_FAULT_RETRY properly has been removed from the -mm tree. Its filename was mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly.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: David Hildenbrand david@redhat.com Subject: mm/madvise: make MADV_POPULATE_(READ|WRITE) handle VM_FAULT_RETRY properly Date: Thu, 14 Mar 2024 17:12:59 +0100

Darrick reports that in some cases where pread() would fail with -EIO and mmap()+access would generate a SIGBUS signal, MADV_POPULATE_READ / MADV_POPULATE_WRITE will keep retrying forever and not fail with -EFAULT.

While the madvise() call can be interrupted by a signal, this is not the desired behavior. MADV_POPULATE_READ / MADV_POPULATE_WRITE should behave like page faults in that case: fail and not retry forever.

A reproducer can be found at [1].

The reason is that __get_user_pages(), as called by faultin_vma_page_range(), will not handle VM_FAULT_RETRY in a proper way: it will simply return 0 when VM_FAULT_RETRY happened, making madvise_populate()->faultin_vma_page_range() retry again and again, never setting FOLL_TRIED->FAULT_FLAG_TRIED for __get_user_pages().

__get_user_pages_locked() does what we want, but duplicating that logic in faultin_vma_page_range() feels wrong.

So let's use __get_user_pages_locked() instead, that will detect VM_FAULT_RETRY and set FOLL_TRIED when retrying, making the fault handler return VM_FAULT_SIGBUS (VM_FAULT_ERROR) at some point, propagating -EFAULT from faultin_page() to __get_user_pages(), all the way to madvise_populate().

But, there is an issue: __get_user_pages_locked() will end up re-taking the MM lock and then __get_user_pages() will do another VMA lookup. In the meantime, the VMA layout could have changed and we'd fail with different error codes than we'd want to.

As __get_user_pages() will currently do a new VMA lookup either way, let it do the VMA handling in a different way, controlled by a new FOLL_MADV_POPULATE flag, effectively moving these checks from madvise_populate() + faultin_page_range() in there.

With this change, Darricks reproducer properly fails with -EFAULT, as documented for MADV_POPULATE_READ / MADV_POPULATE_WRITE.

[1] https://lore.kernel.org/all/20240313171936.GN1927156@frogsfrogsfrogs/

Link: https://lkml.kernel.org/r/20240314161300.382526-1-david@redhat.com Link: https://lkml.kernel.org/r/20240314161300.382526-2-david@redhat.com Fixes: 4ca9b3859dac ("mm/madvise: introduce MADV_POPULATE_(READ|WRITE) to prefault page tables") Signed-off-by: David Hildenbrand david@redhat.com Reported-by: Darrick J. Wong djwong@kernel.org Closes: https://lore.kernel.org/all/20240311223815.GW1927156@frogsfrogsfrogs/ Cc: Darrick J. Wong djwong@kernel.org Cc: Hugh Dickins hughd@google.com Cc: Jason Gunthorpe jgg@nvidia.com Cc: John Hubbard jhubbard@nvidia.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/gup.c | 54 ++++++++++++++++++++++++++++-------------------- mm/internal.h | 10 +++++--- mm/madvise.c | 17 +-------------- 3 files changed, 40 insertions(+), 41 deletions(-)

--- a/mm/gup.c~mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly +++ a/mm/gup.c @@ -1206,6 +1206,22 @@ static long __get_user_pages(struct mm_s

/* first iteration or cross vma bound */ if (!vma || start >= vma->vm_end) { + /* + * MADV_POPULATE_(READ|WRITE) wants to handle VMA + * lookups+error reporting differently. + */ + if (gup_flags & FOLL_MADV_POPULATE) { + vma = vma_lookup(mm, start); + if (!vma) { + ret = -ENOMEM; + goto out; + } + if (check_vma_flags(vma, gup_flags)) { + ret = -EINVAL; + goto out; + } + goto retry; + } vma = gup_vma_lookup(mm, start); if (!vma && in_gate_area(mm, start)) { ret = get_gate_page(mm, start & PAGE_MASK, @@ -1685,35 +1701,35 @@ long populate_vma_page_range(struct vm_a }

/* - * faultin_vma_page_range() - populate (prefault) page tables inside the - * given VMA range readable/writable + * faultin_page_range() - populate (prefault) page tables inside the + * given range readable/writable * * This takes care of mlocking the pages, too, if VM_LOCKED is set. * - * @vma: target vma + * @mm: the mm to populate page tables in * @start: start address * @end: end address * @write: whether to prefault readable or writable * @locked: whether the mmap_lock is still held * - * Returns either number of processed pages in the vma, or a negative error - * code on error (see __get_user_pages()). + * Returns either number of processed pages in the MM, or a negative error + * code on error (see __get_user_pages()). Note that this function reports + * errors related to VMAs, such as incompatible mappings, as expected by + * MADV_POPULATE_(READ|WRITE). * - * vma->vm_mm->mmap_lock must be held. The range must be page-aligned and - * covered by the VMA. If it's released, *@locked will be set to 0. + * The range must be page-aligned. + * + * mm->mmap_lock must be held. If it's released, *@locked will be set to 0. */ -long faultin_vma_page_range(struct vm_area_struct *vma, unsigned long start, - unsigned long end, bool write, int *locked) +long faultin_page_range(struct mm_struct *mm, unsigned long start, + unsigned long end, bool write, int *locked) { - struct mm_struct *mm = vma->vm_mm; unsigned long nr_pages = (end - start) / PAGE_SIZE; int gup_flags; long ret;

VM_BUG_ON(!PAGE_ALIGNED(start)); VM_BUG_ON(!PAGE_ALIGNED(end)); - VM_BUG_ON_VMA(start < vma->vm_start, vma); - VM_BUG_ON_VMA(end > vma->vm_end, vma); mmap_assert_locked(mm);

/* @@ -1725,19 +1741,13 @@ long faultin_vma_page_range(struct vm_ar * a poisoned page. * !FOLL_FORCE: Require proper access permissions. */ - gup_flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_UNLOCKABLE; + gup_flags = FOLL_TOUCH | FOLL_HWPOISON | FOLL_UNLOCKABLE | + FOLL_MADV_POPULATE; if (write) gup_flags |= FOLL_WRITE;

- /* - * We want to report -EINVAL instead of -EFAULT for any permission - * problems or incompatible mappings. - */ - if (check_vma_flags(vma, gup_flags)) - return -EINVAL; - - ret = __get_user_pages(mm, start, nr_pages, gup_flags, - NULL, locked); + ret = __get_user_pages_locked(mm, start, nr_pages, NULL, locked, + gup_flags); lru_add_drain(); return ret; } --- a/mm/internal.h~mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly +++ a/mm/internal.h @@ -686,9 +686,8 @@ struct anon_vma *folio_anon_vma(struct f void unmap_mapping_folio(struct folio *folio); extern long populate_vma_page_range(struct vm_area_struct *vma, unsigned long start, unsigned long end, int *locked); -extern long faultin_vma_page_range(struct vm_area_struct *vma, - unsigned long start, unsigned long end, - bool write, int *locked); +extern long faultin_page_range(struct mm_struct *mm, unsigned long start, + unsigned long end, bool write, int *locked); extern bool mlock_future_ok(struct mm_struct *mm, unsigned long flags, unsigned long bytes);

@@ -1127,10 +1126,13 @@ enum { FOLL_FAST_ONLY = 1 << 20, /* allow unlocking the mmap lock */ FOLL_UNLOCKABLE = 1 << 21, + /* VMA lookup+checks compatible with MADV_POPULATE_(READ|WRITE) */ + FOLL_MADV_POPULATE = 1 << 22, };

#define INTERNAL_GUP_FLAGS (FOLL_TOUCH | FOLL_TRIED | FOLL_REMOTE | FOLL_PIN | \ - FOLL_FAST_ONLY | FOLL_UNLOCKABLE) + FOLL_FAST_ONLY | FOLL_UNLOCKABLE | \ + FOLL_MADV_POPULATE)

/* * Indicates for which pages that are write-protected in the page table, --- a/mm/madvise.c~mm-madvise-make-madv_populate_readwrite-handle-vm_fault_retry-properly +++ a/mm/madvise.c @@ -908,27 +908,14 @@ static long madvise_populate(struct vm_a { const bool write = behavior == MADV_POPULATE_WRITE; struct mm_struct *mm = vma->vm_mm; - unsigned long tmp_end; int locked = 1; long pages;

*prev = vma;

while (start < end) { - /* - * We might have temporarily dropped the lock. For example, - * our VMA might have been split. - */ - if (!vma || start >= vma->vm_end) { - vma = vma_lookup(mm, start); - if (!vma) - return -ENOMEM; - } - - tmp_end = min_t(unsigned long, end, vma->vm_end); /* Populate (prefault) page tables readable/writable. */ - pages = faultin_vma_page_range(vma, start, tmp_end, write, - &locked); + pages = faultin_page_range(mm, start, end, write, &locked); if (!locked) { mmap_read_lock(mm); locked = 1; @@ -949,7 +936,7 @@ static long madvise_populate(struct vm_a pr_warn_once("%s: unhandled return value: %ld\n", __func__, pages); fallthrough; - case -ENOMEM: + case -ENOMEM: /* No VMA or out of memory. */ return -ENOMEM; } } _

Patches currently in -mm which might be from david@redhat.com are

mm-madvise-dont-perform-madvise-vma-walk-for-madv_populate_readwrite.patch mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared.patch mm-convert-folio_estimated_sharers-to-folio_likely_mapped_shared-fix.patch selftests-memfd_secret-add-vmsplice-test.patch mm-merge-folio_is_secretmem-and-folio_fast_pin_allowed-into-gup_fast_folio_allowed.patch mm-optimize-config_per_vma_lock-member-placement-in-vm_area_struct.patch mm-remove-prot-parameter-from-move_pte.patch mm-gup-consistently-name-gup-fast-functions.patch mm-treewide-rename-config_have_fast_gup-to-config_have_gup_fast.patch mm-use-gup-fast-instead-fast-gup-in-remaining-comments.patch drivers-virt-acrn-fix-pfnmap-pte-checks-in-acrn_vm_ram_map.patch mm-pass-vma-instead-of-mm-to-follow_pte.patch mm-follow_pte-improvements.patch mm-allow-for-detecting-underflows-with-page_mapcount-again.patch mm-rmap-always-inline-anon-file-rmap-duplication-of-a-single-pte.patch mm-rmap-add-fast-path-for-small-folios-when-adding-removing-duplicating.patch mm-track-mapcount-of-large-folios-in-single-value.patch mm-improve-folio_likely_mapped_shared-using-the-mapcount-of-large-folios.patch mm-make-folio_mapcount-return-0-for-small-typed-folios.patch mm-memory-use-folio_mapcount-in-zap_present_folio_ptes.patch mm-huge_memory-use-folio_mapcount-in-zap_huge_pmd-sanity-check.patch mm-memory-failure-use-folio_mapcount-in-hwpoison_user_mappings.patch mm-page_alloc-use-folio_mapped-in-__alloc_contig_migrate_range.patch mm-migrate-use-folio_likely_mapped_shared-in-add_page_for_migration.patch sh-mm-cache-use-folio_mapped-in-copy_from_user_page.patch mm-filemap-use-folio_mapcount-in-filemap_unaccount_folio.patch mm-migrate_device-use-folio_mapcount-in-migrate_vma_check_page.patch trace-events-page_ref-trace-the-raw-page-mapcount-value.patch xtensa-mm-convert-check_tlb_entry-to-sanity-check-folios.patch mm-debug-print-only-page-mapcount-excluding-folio-entire-mapcount-in-__dump_folio.patch documentation-admin-guide-cgroup-v1-memoryrst-dont-reference-page_mapcount.patch mm-ksm-rename-get_ksm_page_flags-to-ksm_get_folio_flags.patch mm-ksm-remove-page_mapcount-usage-in-stable_tree_search.patch loongarch-tlb-fix-error-parameter-ptep-set-but-not-used-due-to-__tlb_remove_tlb_entry.patch