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From: Konstantin Belousov <kib@FreeBSD.org>
Date: Mon, 17 Aug 2009 13:27:55 +0000 (UTC)
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Subject: cvs commit: src/sys/amd64/amd64 pmap.c
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kib         2009-08-17 13:27:55 UTC

  FreeBSD src repository

  Modified files:
    sys/amd64/amd64      pmap.c 
  Log:
  SVN rev 196318 on 2009-08-17 13:27:55Z by kib
  
  Correct a critical accounting error in pmap_demote_pde().  Specifically,
  when pmap_demote_pde() allocates a page table page to implement a
  user-space demotion, it must increment the pmap's resident page count.
  Not doing so, can lead to an underflow during address space termination
  that causes pmap_remove() to exit prematurely, before it has destroyed
  all of the mappings within the specified range.  The ultimate effect or
  symptom of this error is an assertion failure in vm_page_free_toq()
  because the page being freed is still mapped.
  
  This error is only possible when superpage promotion is enabled.  Thus,
  it only affects FreeBSD  versions greater than 7.2.
  
  Tested by:      pho, alc
  Reviewed by:    alc
  Approved by:    re (rwatson)
  MFC after:      1 week
  
  Revision  Changes    Path
  1.668     +2 -0      src/sys/amd64/amd64/pmap.c