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bh=GjynOfmK1NGfPSqaN7twnNbL6ZbrLMDmUL3fGSYghrQ=; b=Gz/FIouAmAk3lPMsguNusNFUWx9llS9J52qhGrdcRtU8VwHrSr1oxvpD5TnsfPz2q8exXE KZwmcMUBYPNOl/K5EzZH5q5zWfmWQ4tDNFjrFF/pIKLQWErqznhiNjzrT8c+cJWfbb6O9t Gd2xQUGnAmuS77NUOSLb33IyX1X8Ee0= X-Rspamd-Queue-Id: 9B4704000A X-Rspam-User: Authentication-Results: imf04.hostedemail.com; dkim=pass header.d=oracle.com header.s=corp-2022-7-12 header.b=T6CtDUcI; dkim=pass header.d=oracle.onmicrosoft.com header.s=selector2-oracle-onmicrosoft-com header.b=OrN4TMMq; dmarc=pass (policy=none) header.from=oracle.com; arc=pass ("microsoft.com:s=arcselector9901:i=1"); spf=pass (imf04.hostedemail.com: domain of mike.kravetz@oracle.com designates 205.220.177.32 as permitted sender) smtp.mailfrom=mike.kravetz@oracle.com X-Rspamd-Server: rspam06 X-Stat-Signature: zh9w5jp18e8ffoo4t565jn7wk83uqxm5 X-HE-Tag: 1668470125-938549 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: madvise(MADV_DONTNEED) ends up calling zap_page_range() to clear page tables associated with the address range. For hugetlb vmas, zap_page_range will call __unmap_hugepage_range_final. However, __unmap_hugepage_range_final assumes the passed vma is about to be removed and deletes the vma_lock to prevent pmd sharing as the vma is on the way out. In the case of madvise(MADV_DONTNEED) the vma remains, but the missing vma_lock prevents pmd sharing and could potentially lead to issues with truncation/fault races. This issue was originally reported here [1] as a BUG triggered in page_try_dup_anon_rmap. Prior to the introduction of the hugetlb vma_lock, __unmap_hugepage_range_final cleared the VM_MAYSHARE flag to prevent pmd sharing. Subsequent faults on this vma were confused as VM_MAYSHARE indicates a sharable vma, but was not set so page_mapping was not set in new pages added to the page table. This resulted in pages that appeared anonymous in a VM_SHARED vma and triggered the BUG. Address issue by adding a new zap flag ZAP_FLAG_UNMAP to indicate an unmap call from unmap_vmas(). This is used to indicate the 'final' unmapping of a hugetlb vma. When called via MADV_DONTNEED, this flag is not set and the vm_lock is not deleted. [1] https://lore.kernel.org/lkml/CAO4mrfdLMXsao9RF4fUE8-Wfde8xmjsKrTNMNC9wjUb6JudD0g@mail.gmail.com/ Fixes: 90e7e7f5ef3f ("mm: enable MADV_DONTNEED for hugetlb mappings") Signed-off-by: Mike Kravetz Reported-by: Wei Chen Cc: --- include/linux/mm.h | 2 ++ mm/hugetlb.c | 27 ++++++++++++++++----------- mm/memory.c | 2 +- 3 files changed, 19 insertions(+), 12 deletions(-) diff --git a/include/linux/mm.h b/include/linux/mm.h index dd5a38682537..a4e24dd2d96e 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1886,6 +1886,8 @@ struct zap_details { * default, the flag is not set. */ #define ZAP_FLAG_DROP_MARKER ((__force zap_flags_t) BIT(0)) +/* Set in unmap_vmas() to indicate a final unmap call. Only used by hugetlb */ +#define ZAP_FLAG_UNMAP ((__force zap_flags_t) BIT(1)) #ifdef CONFIG_MMU extern bool can_do_mlock(void); diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 9d765364231e..7559b9dfe782 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -5210,17 +5210,22 @@ void __unmap_hugepage_range_final(struct mmu_gather *tlb, __unmap_hugepage_range(tlb, vma, start, end, ref_page, zap_flags); - /* - * Unlock and free the vma lock before releasing i_mmap_rwsem. When - * the vma_lock is freed, this makes the vma ineligible for pmd - * sharing. And, i_mmap_rwsem is required to set up pmd sharing. - * This is important as page tables for this unmapped range will - * be asynchrously deleted. If the page tables are shared, there - * will be issues when accessed by someone else. - */ - __hugetlb_vma_unlock_write_free(vma); - - i_mmap_unlock_write(vma->vm_file->f_mapping); + if (zap_flags & ZAP_FLAG_UNMAP) { /* final unmap */ + /* + * Unlock and free the vma lock before releasing i_mmap_rwsem. + * When the vma_lock is freed, this makes the vma ineligible + * for pmd sharing. And, i_mmap_rwsem is required to set up + * pmd sharing. This is important as page tables for this + * unmapped range will be asynchrously deleted. If the page + * tables are shared, there will be issues when accessed by + * someone else. + */ + __hugetlb_vma_unlock_write_free(vma); + i_mmap_unlock_write(vma->vm_file->f_mapping); + } else { + i_mmap_unlock_write(vma->vm_file->f_mapping); + hugetlb_vma_unlock_write(vma); + } } void unmap_hugepage_range(struct vm_area_struct *vma, unsigned long start, diff --git a/mm/memory.c b/mm/memory.c index a177f6bbfafc..6d77bc00bca1 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1673,7 +1673,7 @@ void unmap_vmas(struct mmu_gather *tlb, struct maple_tree *mt, { struct mmu_notifier_range range; struct zap_details details = { - .zap_flags = ZAP_FLAG_DROP_MARKER, + .zap_flags = ZAP_FLAG_DROP_MARKER | ZAP_FLAG_UNMAP, /* Careful - we need to zap private pages too! */ .even_cows = true, };