• Yang Shi's avatar
    mm: filemap: check if THP has hwpoisoned subpage for PMD page fault · eac96c3e
    Yang Shi authored
    When handling shmem page fault the THP with corrupted subpage could be
    PMD mapped if certain conditions are satisfied.  But kernel is supposed
    to send SIGBUS when trying to map hwpoisoned page.
    
    There are two paths which may do PMD map: fault around and regular
    fault.
    
    Before commit f9ce0be7 ("mm: Cleanup faultaround and finish_fault()
    codepaths") the thing was even worse in fault around path.  The THP
    could be PMD mapped as long as the VMA fits regardless what subpage is
    accessed and corrupted.  After this commit as long as head page is not
    corrupted the THP could be PMD mapped.
    
    In the regular fault path the THP could be PMD mapped as long as the
    corrupted page is not accessed and the VMA fits.
    
    This loophole could be fixed by iterating every subpage to check if any
    of them is hwpoisoned or not, but it is somewhat costly in page fault
    path.
    
    So introduce a new page flag called HasHWPoisoned on the first tail
    page.  It indicates the THP has hwpoisoned subpage(s).  It is set if any
    subpage of THP is found hwpoisoned by memory failure and after the
    refcount is bumped successfully, then cleared when the THP is freed or
    split.
    
    The soft offline path doesn't need this since soft offline handler just
    marks a subpage hwpoisoned when the subpage is migrated successfully.
    But shmem THP didn't get split then migrated at all.
    
    Link: https://lkml.kernel.org/r/20211020210755.23964-3-shy828301@gmail.com
    Fixes: 800d8c63 ("shmem: add huge pages support")
    Signed-off-by: default avatarYang Shi <shy828301@gmail.com>
    Reviewed-by: default avatarNaoya Horiguchi <naoya.horiguchi@nec.com>
    Suggested-by: default avatarKirill A. Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Hugh Dickins <hughd@google.com>
    Cc: Matthew Wilcox <willy@infradead.org>
    Cc: Oscar Salvador <osalvador@suse.de>
    Cc: Peter Xu <peterx@redhat.com>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    eac96c3e
memory.c 149 KB