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badpage: vm_normal_page use print_bad_pte
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: Hugh Dickins <[email protected]> Cc: Nick Piggin <[email protected]> Cc: Christoph Lameter <[email protected]> Cc: Mel Gorman <[email protected]> Cc: Rik van Riel <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
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