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| H A D | dax.c | 06083a09 Fri Apr 29 01:16:10 CDT 2022 Muchun Song <songmuchun@bytedance.com> dax: fix missing writeprotect the pte entry
Currently dax_mapping_entry_mkclean() fails to clean and write protect the
pte entry within a DAX PMD entry during an *sync operation. This can
result in data loss in the following sequence:
1) process A mmap write to DAX PMD, dirtying PMD radix tree entry and
making the pmd entry dirty and writeable.
2) process B mmap with the @offset (e.g. 4K) and @length (e.g. 4K)
write to the same file, dirtying PMD radix tree entry (already
done in 1)) and making the pte entry dirty and writeable.
3) fsync, flushing out PMD data and cleaning the radix tree entry. We
currently fail to mark the pte entry as clean and write protected
since the vma of process B is not covered in dax_entry_mkclean().
4) process B writes to the pte. These don't cause any page faults since
the pte entry is dirty and writeable. The radix tree entry remains
clean.
5) fsync, which fails to flush the dirty PMD data because the radix tree
entry was clean.
6) crash - dirty data that should have been fsync'd as part of 5) could
still have been in the processor cache, and is lost.
Just to use pfn_mkclean_range() to clean the pfns to fix this issue.
Link: https://lkml.kernel.org/r/20220403053957.10770-6-songmuchun@bytedance.com
Fixes: 4b4bb46d00b3 ("dax: clear dirty entry tags on cache flush")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Alistair Popple <apopple@nvidia.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Jan Kara <jack@suse.cz>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Ralph Campbell <rcampbell@nvidia.com>
Cc: Ross Zwisler <zwisler@kernel.org>
Cc: Xiongchun Duan <duanxiongchun@bytedance.com>
Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
Cc: Yang Shi <shy828301@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
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