From: Jan Kara jack@suse.cz Subject: mm/memory.c: fix modifying of page protection by insert_pfn()

Aneesh has reported that PPC triggers the following warning when excercising DAX code:

[c00000000007610c] set_pte_at+0x3c/0x190 LR [c000000000378628] insert_pfn+0x208/0x280 Call Trace: [c0000002125df980] [8000000000000104] 0x8000000000000104 (unreliable) [c0000002125df9c0] [c000000000378488] insert_pfn+0x68/0x280 [c0000002125dfa30] [c0000000004a5494] dax_iomap_pte_fault.isra.7+0x734/0xa40 [c0000002125dfb50] [c000000000627250] __xfs_filemap_fault+0x280/0x2d0 [c0000002125dfbb0] [c000000000373abc] do_wp_page+0x48c/0xa40 [c0000002125dfc00] [c000000000379170] __handle_mm_fault+0x8d0/0x1fd0 [c0000002125dfd00] [c00000000037a9b0] handle_mm_fault+0x140/0x250 [c0000002125dfd40] [c000000000074bb0] __do_page_fault+0x300/0xd60 [c0000002125dfe20] [c00000000000acf4] handle_page_fault+0x18

Now that is WARN_ON in set_pte_at which is

VM_WARN_ON(pte_hw_valid(*ptep) && !pte_protnone(*ptep));

The problem is that on some architectures set_pte_at() cannot cope with a situation where there is already some (different) valid entry present.

Use ptep_set_access_flags() instead to modify the pfn which is built to deal with modifying existing PTE.

Link: http://lkml.kernel.org/r/20190311084537.16029-1-jack@suse.cz Fixes: b2770da64254 "mm: add vm_insert_mixed_mkwrite()" Signed-off-by: Jan Kara jack@suse.cz Reported-by: "Aneesh Kumar K.V" aneesh.kumar@linux.ibm.com Reviewed-by: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Acked-by: Dan Williams dan.j.williams@intel.com Cc: Chandan Rajendra chandan@linux.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

mm/memory.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/mm/memory.c~mm-fix-modifying-of-page-protection-by-insert_pfn +++ a/mm/memory.c @@ -1549,10 +1549,12 @@ static vm_fault_t insert_pfn(struct vm_a WARN_ON_ONCE(!is_zero_pfn(pte_pfn(*pte))); goto out_unlock; } - entry = *pte; - goto out_mkwrite; - } else - goto out_unlock; + entry = pte_mkyoung(*pte); + entry = maybe_mkwrite(pte_mkdirty(entry), vma); + if (ptep_set_access_flags(vma, addr, pte, entry, 1)) + update_mmu_cache(vma, addr, pte); + } + goto out_unlock; }

/* Ok, finally just insert the thing.. */ @@ -1561,7 +1563,6 @@ static vm_fault_t insert_pfn(struct vm_a else entry = pte_mkspecial(pfn_t_pte(pfn, prot));

-out_mkwrite: if (mkwrite) { entry = pte_mkyoung(entry); entry = maybe_mkwrite(pte_mkdirty(entry), vma); _