From: Qiujun Huang <hqjagain@xxxxxxxxx> Subject: mm: fix gup_pud_range sorry for not processing for a long time. I met it again. patch v1 https://lkml.org/lkml/2019/9/20/656 do_machine_check() do_memory_failure() memory_failure() hw_poison_user_mappings() try_to_unmap() pteval = swp_entry_to_pte(make_hwpoison_entry(subpage)); ...and now we have a swap entry that indicates that the page entry refers to a bad (and poisoned) page of memory, but gup_fast() at this level of the page table was ignoring swap entries, and incorrectly assuming that "!pxd_none() == valid and present". And this was not just a poisoned page problem, but a generaly swap entry problem. So, any swap entry type (device memory migration, numa migration, or just regular swapping) could lead to the same problem. Fix this by checking for pxd_present(), instead of pxd_none(). Link: http://lkml.kernel.org/r/1578479084-15508-1-git-send-email-hqjagain@xxxxxxxxx Signed-off-by: Qiujun Huang <hqjagain@xxxxxxxxx> Cc: John Hubbard <jhubbard@xxxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Naoya Horiguchi <n-horiguchi@xxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/gup.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/mm/gup.c~mm-fix-gup_pud_range +++ a/mm/gup.c @@ -2237,7 +2237,7 @@ static int gup_pud_range(p4d_t p4d, unsi pud_t pud = READ_ONCE(*pudp); next = pud_addr_end(addr, end); - if (pud_none(pud)) + if (unlikely(!pud_present(pud))) return 0; if (unlikely(pud_huge(pud))) { if (!gup_huge_pud(pud, pudp, addr, next, flags, _
