1. 26 Sep, 2016 39 commits
  2. 25 Sep, 2016 1 commit
    • Lorenzo Stoakes's avatar
      mm: check VMA flags to avoid invalid PROT_NONE NUMA balancing · 38e08854
      Lorenzo Stoakes authored
      The NUMA balancing logic uses an arch-specific PROT_NONE page table flag
      defined by pte_protnone() or pmd_protnone() to mark PTEs or huge page
      PMDs respectively as requiring balancing upon a subsequent page fault.
      User-defined PROT_NONE memory regions which also have this flag set will
      not normally invoke the NUMA balancing code as do_page_fault() will send
      a segfault to the process before handle_mm_fault() is even called.
      
      However if access_remote_vm() is invoked to access a PROT_NONE region of
      memory, handle_mm_fault() is called via faultin_page() and
      __get_user_pages() without any access checks being performed, meaning
      the NUMA balancing logic is incorrectly invoked on a non-NUMA memory
      region.
      
      A simple means of triggering this problem is to access PROT_NONE mmap'd
      memory using /proc/self/mem which reliably results in the NUMA handling
      functions being invoked when CONFIG_NUMA_BALANCING is set.
      
      This issue was reported in bugzilla (issue 99101) which includes some
      simple repro code.
      
      There are BUG_ON() checks in do_numa_page() and do_huge_pmd_numa_page()
      added at commit c0e7cad9 to avoid accidentally provoking strange
      behaviour by attempting to apply NUMA balancing to pages that are in
      fact PROT_NONE.  The BUG_ON()'s are consistently triggered by the repro.
      
      This patch moves the PROT_NONE check into mm/memory.c rather than
      invoking BUG_ON() as faulting in these pages via faultin_page() is a
      valid reason for reaching the NUMA check with the PROT_NONE page table
      flag set and is therefore not always a bug.
      
      Link: https://bugzilla.kernel.org/show_bug.cgi?id=99101Reported-by: default avatarTrevor Saunders <tbsaunde@tbsaunde.org>
      Signed-off-by: default avatarLorenzo Stoakes <lstoakes@gmail.com>
      Acked-by: default avatarRik van Riel <riel@redhat.com>
      Cc: Andrew Morton <akpm@linux-foundation.org>
      Cc: Mel Gorman <mgorman@techsingularity.net>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      38e08854