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    • Hugh Dickins's avatar
      x86: fix PAE pmd_bad bootup warning · aeed5fce
      Hugh Dickins authored
      
      Fix warning from pmd_bad() at bootup on a HIGHMEM64G HIGHPTE x86_32.
      
      That came from 9fc34113 x86: debug pmd_bad();
      but we understand now that the typecasting was wrong for PAE in the previous
      version: pagetable pages above 4GB looked bad and stopped Arjan from booting.
      
      And revert that cded932b x86: fix pmd_bad
      and pud_bad to support huge pages.  It was the wrong way round: we shouldn't
      weaken every pmd_bad and pud_bad check to let huge pages slip through - in
      part they check that we _don't_ have a huge page where it's not expected.
      
      Put the x86 pmd_bad() and pud_bad() definitions back to what they have long
      been: they can be improved (x86_32 should use PTE_MASK, to stop PAE thinking
      junk in the upper word is good; and x86_64 should follow x86_32's stricter
      comparison, to stop thinking any subset of required bits is good); but that
      should be a later patch.
      
      Fix Hans' good observation that follow_page() will never find pmd_huge()
      because that would have already failed the pmd_bad test: test pmd_huge in
      between the pmd_none and pmd_bad tests.  Tighten x86's pmd_huge() check?
      No, once it's a hugepage entry, it can get quite far from a good pmd: for
      example, PROT_NONE leaves it with only ACCESSED of the KERN_PGTABLE bits.
      
      However... though follow_page() contains this and another test for huge
      pages, so it's nice to keep it working on them, where does it actually get
      called on a huge page?  get_user_pages() checks is_vm_hugetlb_page(vma) to
      to call alternative hugetlb processing, as does unmap_vmas() and others.
      
      Signed-off-by: default avatarHugh Dickins <hugh@veritas.com>
      Earlier-version-tested-by: default avatarIngo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Jeff Chua <jeff.chua.linux@gmail.com>
      Cc: Hans Rosenfeld <hans.rosenfeld@amd.com>
      Cc: Arjan van de Ven <arjan@linux.intel.com>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      aeed5fce
  7. May 05, 2008
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