mm: make page_mapped_in_vma() hugetlb walk aware

When a process consumes a UE in a page, the memory failure handler
attempts to collect information for a potential SIGBUS.  If the page is an
anonymous page, page_mapped_in_vma(page, vma) is invoked in order to

  1. retrieve the vaddr from the process' address space,

  2. verify that the vaddr is indeed mapped to the poisoned page,
     where 'page' is the precise small page with UE.

It's been observed that when injecting poison to a non-head subpage of an
anonymous hugetlb page, no SIGBUS shows up, while injecting to the head
page produces a SIGBUS.  The cause is that, though hugetlb_walk() returns
a valid pmd entry (on x86), but check_pte() detects mismatch between the
head page per the pmd and the input subpage.  Thus the vaddr is considered
not mapped to the subpage and the process is not collected for SIGBUS
purpose.  This is the calling stack:

      collect_procs_anon
        page_mapped_in_vma
          page_vma_mapped_walk
            hugetlb_walk
              huge_pte_lock
                check_pte

check_pte() header says that it
"check if [pvmw->pfn, @pvmw->pfn + @pvmw->nr_pages) is mapped at the @pvmw->pte"
but practically works only if pvmw->pfn is the head page pfn at pvmw->pte.
Hindsight acknowledging that some pvmw->pte could point to a hugepage of
some sort such that it makes sense to make check_pte() work for hugepage.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Jane Chu <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Kirill A. Shuemov <[email protected]>
Cc: linmiaohe <[email protected]>
Cc: Matthew Wilcow (Oracle) <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
(cherry picked from commit 442b1eca223b4860cc85ef970ae602d125aec5a4)

Conflicts:
	mm/page_vma_mapped.c
Conflict due to lack of upstream commits
  9651eea ("mm: correct stale comment of function check_pte")
  2aff7a4 ("mm: Convert page_vma_mapped_walk to work on PFNs")
  8f0b747 ("mm/page_vma_mapped.c: use helper function huge_pte_lock")
not backporting them because #1 and #3 are trivial, #2 involves more
code than the issue this patch is addressing.
The change here in the backport works in the same spirit with minimal impact.

Orabug: 37956589

Signed-off-by: Jane Chu <[email protected]>
Reviewed-by: William Roche <[email protected]>
Signed-off-by: Vijayendra Suman <[email protected]>

Author: jchu314atgithub

mm/page_vma_mapped.c

@@ -116,7 +116,9 @@ static bool check_pte(struct page_vma_mapped_walk *pvmw)
 		pfn = pte_pfn(*pvmw->pte);
 	}
 
-	return pfn_is_match(pvmw->page, pfn);
+	if (unlikely(PageHuge(pvmw->page)))
+		return pfn_is_match(compound_head(pvmw->page), pfn);
+	return pfn_is_match((pvmw->page), pfn);
 }
 
 static void step_forward(struct page_vma_mapped_walk *pvmw, unsigned long size)