dax: fix __dax_pmd_fault crash
Since 4.3 introduced devm_memremap_pages() the pfns handled by DAX may optionally have a struct page backing. When a mapped pfn reaches vmf_insert_pfn_pmd() it fails with a crash signature like the following: kernel BUG at mm/huge_memory.c:905! [..] Call Trace: [<ffffffff812a73ba>] __dax_pmd_fault+0x2ea/0x5b0 [<ffffffffa01a4182>] xfs_filemap_pmd_fault+0x92/0x150 [xfs] [<ffffffff811fbe02>] handle_mm_fault+0x312/0x1b50 Fix this by falling back to 4K mappings in the pfn_valid() case. Longer term, vmf_insert_pfn_pmd() needs to grow support for architectures that can provide a 'pmd_special' capability. Cc: <stable@vger.kernel.org> Cc: Andrew Morton <akpm@linux-foundation.org> Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
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fs/dax.c
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fs/dax.c
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@ -627,6 +627,13 @@ int __dax_pmd_fault(struct vm_area_struct *vma, unsigned long address,
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if ((length < PMD_SIZE) || (pfn & PG_PMD_COLOUR))
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goto fallback;
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/*
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* TODO: teach vmf_insert_pfn_pmd() to support
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* 'pte_special' for pmds
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*/
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if (pfn_valid(pfn))
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goto fallback;
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if (buffer_unwritten(&bh) || buffer_new(&bh)) {
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int i;
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for (i = 0; i < PTRS_PER_PMD; i++)
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