The patch titled Subject: hugetlbfs: clear resv_map pointer if mmap fails has been added to the -mm mm-hotfixes-unstable branch. Its filename is hugetlbfs-clear-resv_map-pointer-if-mmap-fails.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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: Rik van Riel riel@surriel.com Subject: hugetlbfs: clear resv_map pointer if mmap fails Date: Thu, 5 Oct 2023 23:59:06 -0400

Patch series "hugetlbfs: close race between MADV_DONTNEED and page fault", v7.

Malloc libraries, like jemalloc and tcalloc, take decisions on when to call madvise independently from the code in the main application.

This sometimes results in the application page faulting on an address, right after the malloc library has shot down the backing memory with MADV_DONTNEED.

Usually this is harmless, because we always have some 4kB pages sitting around to satisfy a page fault. However, with hugetlbfs systems often allocate only the exact number of huge pages that the application wants.

Due to TLB batching, hugetlbfs MADV_DONTNEED will free pages outside of any lock taken on the page fault path, which can open up the following race condition:

CPU 1 CPU 2

MADV_DONTNEED unmap page shoot down TLB entry page fault fail to allocate a huge page killed with SIGBUS free page

Fix that race by extending the hugetlb_vma_lock locking scheme to also cover private hugetlb mappings (with resv_map), and pulling the locking from __unmap_hugepage_final_range into helper functions called from zap_page_range_single. This ensures page faults stay locked out of the MADV_DONTNEED VMA until the huge pages have actually been freed.

This patch (of 3):

Hugetlbfs leaves a dangling pointer in the VMA if mmap fails. This has not been a problem so far, but other code in this patch series tries to follow that pointer.

Link: https://lkml.kernel.org/r/20231006040020.3677377-1-riel@surriel.com Link: https://lkml.kernel.org/r/20231006040020.3677377-2-riel@surriel.com Fixes: 04ada095dcfc ("hugetlb: don't delete vma_lock in hugetlb MADV_DONTNEED processing") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Signed-off-by: Rik van Riel riel@surriel.com Cc: Matthew Wilcox (Oracle) willy@infradead.org Cc: Muchun Song muchun.song@linux.dev Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/hugetlb.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-)

--- a/mm/hugetlb.c~hugetlbfs-clear-resv_map-pointer-if-mmap-fails +++ a/mm/hugetlb.c @@ -1138,8 +1138,7 @@ static void set_vma_resv_map(struct vm_a VM_BUG_ON_VMA(!is_vm_hugetlb_page(vma), vma); VM_BUG_ON_VMA(vma->vm_flags & VM_MAYSHARE, vma);

- set_vma_private_data(vma, (get_vma_private_data(vma) & - HPAGE_RESV_MASK) | (unsigned long)map); + set_vma_private_data(vma, (unsigned long)map); }

static void set_vma_resv_flags(struct vm_area_struct *vma, unsigned long flags) @@ -6811,8 +6810,10 @@ out_err: */ if (chg >= 0 && add < 0) region_abort(resv_map, from, to, regions_needed); - if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) + if (vma && is_vma_resv_set(vma, HPAGE_RESV_OWNER)) { kref_put(&resv_map->refs, resv_map_release); + set_vma_resv_map(vma, NULL); + } return false; }

_

Patches currently in -mm which might be from riel@surriel.com are

hugetlbfs-clear-resv_map-pointer-if-mmap-fails.patch hugetlbfs-extend-hugetlb_vma_lock-to-private-vmas.patch hugetlbfs-close-race-between-madv_dontneed-and-page-fault.patch