• Hugh Dickins's avatar
    [PATCH] hugetlb: prepare_hugepage_range check offset too · 68589bc3
    Hugh Dickins authored
    
    
    (David:)
    
    If hugetlbfs_file_mmap() returns a failure to do_mmap_pgoff() - for example,
    because the given file offset is not hugepage aligned - then do_mmap_pgoff
    will go to the unmap_and_free_vma backout path.
    
    But at this stage the vma hasn't been marked as hugepage, and the backout path
    will call unmap_region() on it.  That will eventually call down to the
    non-hugepage version of unmap_page_range().  On ppc64, at least, that will
    cause serious problems if there are any existing hugepage pagetable entries in
    the vicinity - for example if there are any other hugepage mappings under the
    same PUD.  unmap_page_range() will trigger a bad_pud() on the hugepage pud
    entries.  I suspect this will also cause bad problems on ia64, though I don't
    have a machine to test it on.
    
    (Hugh:)
    
    prepare_hugepage_range() should check file offset alignment when it checks
    virtual address and length, to stop MAP_FIXED with a bad huge offset from
    unmapping before it fails further down.  PowerPC should apply the same
    prepare_hugepage_range alignment checks as ia64 and all the others do.
    
    Then none of the alignment checks in hugetlbfs_file_mmap are required (nor
    is the check for too small a mapping); but even so, move up setting of
    VM_HUGETLB and add a comment to warn of what David Gibson discovered - if
    hugetlbfs_file_mmap fails before setting it, do_mmap_pgoff's unmap_region
    when unwinding from error will go the non-huge way, which may cause bad
    behaviour on architectures (powerpc and ia64) which segregate their huge
    mappings into a separate region of the address space.
    Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
    Cc: "Luck, Tony" <tony.luck@intel.com>
    Cc: "David S. Miller" <davem@davemloft.net>
    Acked-by: default avatarAdam Litke <agl@us.ibm.com>
    Acked-by: default avatarDavid Gibson <david@gibson.dropbear.id.au>
    Cc: Paul Mackerras <paulus@samba.org>
    Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
    Signed-off-by: default avatarAndrew Morton <akpm@osdl.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@osdl.org>
    68589bc3
hugetlb.h 5.63 KB