• Nishanth Aravamudan's avatar
    hugetlb: ensure hugepage access is denied if hugepages are not supported · 457c1b27
    Nishanth Aravamudan authored
    Currently, I am seeing the following when I `mount -t hugetlbfs /none
    /dev/hugetlbfs`, and then simply do a `ls /dev/hugetlbfs`.  I think it's
    related to the fact that hugetlbfs is properly not correctly setting
    itself up in this state?:
      Unable to handle kernel paging request for data at address 0x00000031
      Faulting instruction address: 0xc000000000245710
      Oops: Kernel access of bad area, sig: 11 [#1]
      SMP NR_CPUS=2048 NUMA pSeries
    In KVM guests on Power, in a guest not backed by hugepages, we see the
      AnonHugePages:         0 kB
      HugePages_Total:       0
      HugePages_Free:        0
      HugePages_Rsvd:        0
      HugePages_Surp:        0
      Hugepagesize:         64 kB
    HPAGE_SHIFT == 0 in this configuration, which indicates that hugepages
    are not supported at boot-time, but this is only checked in
    hugetlb_init().  Extract the check to a helper function, and use it in a
    few relevant places.
    This does make hugetlbfs not supported (not registered at all) in this
    environment.  I believe this is fine, as there are no valid hugepages
    and that won't change at runtime.
    [akpm@linux-foundation.org: use pr_info(), per Mel]
    [akpm@linux-foundation.org: fix build when HPAGE_SHIFT is undefined]
    Signed-off-by: default avatarNishanth Aravamudan <nacc@linux.vnet.ibm.com>
    Reviewed-by: default avatarAneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Acked-by: default avatarMel Gorman <mgorman@suse.de>
    Cc: Randy Dunlap <rdunlap@infradead.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>