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    badpage: vm_normal_page use print_bad_pte · 22b31eec
    Hugh Dickins 提交于
    print_bad_pte() is so far being called only when zap_pte_range() finds
    negative page_mapcount, or there's a fault on a pte_file where it does not
    belong.  That's weak coverage when we suspect pagetable corruption.
    
    Originally, it was called when vm_normal_page() found an invalid pfn: but
    pfn_valid is expensive on some architectures and configurations, so 2.6.24
    put that under CONFIG_DEBUG_VM (which doesn't help in the field), then
    2.6.26 replaced it by a VM_BUG_ON (likewise).
    
    Reinstate the print_bad_pte() in vm_normal_page(), but use a cheaper test
    than pfn_valid(): memmap_init_zone() (used in bootup and hotplug) keep a
    __read_mostly note of the highest_memmap_pfn, vm_normal_page() then check
    pfn against that.  We could call this pfn_plausible() or pfn_sane(), but I
    doubt we'll need it elsewhere: of course it's not reliable, but gives much
    stronger pagetable validation on many boxes.
    
    Also use print_bad_pte() when the pte_special bit is found outside a
    VM_PFNMAP or VM_MIXEDMAP area, instead of VM_BUG_ON.
    Signed-off-by: NHugh Dickins <hugh@veritas.com>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Christoph Lameter <cl@linux-foundation.org>
    Cc: Mel Gorman <mel@csn.ul.ie>
    Cc: Rik van Riel <riel@redhat.com>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    22b31eec
internal.h 7.8 KB