cvs commit: src/sys/amd64/amd64 pmap.c src/sys/i386/i386 pmap.c src/sys/sparc64/include pmap.h src/sys/vm pmap.h

[Alan Cox]

alc         2006-07-20 17:48:41 UTC

  FreeBSD src repository

  Modified files:
    sys/amd64/amd64      pmap.c 
    sys/i386/i386        pmap.c 
    sys/sparc64/include  pmap.h 
    sys/vm               pmap.h 
  Log:
  Add pmap_clear_write() to the interface between the virtual memory
  system's machine-dependent and machine-independent layers.  Once
  pmap_clear_write() is implemented on all of our supported
  architectures, I intend to replace all calls to pmap_page_protect() by
  calls to pmap_clear_write().  Why?  Both the use and implementation of
  pmap_page_protect() in our virtual memory system has subtle errors,
  specifically, the management of execute permission is broken on some
  architectures.  The "prot" argument to pmap_page_protect() should
  behave differently from the "prot" argument to other pmap functions.
  Instead of meaning, "give the specified access rights to all of the
  physical page's mappings," it means "don't take away the specified
  access rights from all of the physical page's mappings, but do take
  away the ones that aren't specified."  However, owing to our i386
  legacy, i.e., no support for no-execute rights, all but one invocation
  of pmap_page_protect() specifies VM_PROT_READ only, when the intent
  is, in fact, to remove only write permission.  Consequently, a
  faithful implementation of pmap_page_protect(), e.g., ia64, would
  remove execute permission as well as write permission.  On the other
  hand, some architectures that support execute permission have
  basically ignored whether or not VM_PROT_EXECUTE is passed to
  pmap_page_protect(), e.g., amd64 and sparc64.  This change represents
  the first step in replacing pmap_page_protect() by the less subtle
  pmap_clear_write() that is already implemented on amd64, i386, and
  sparc64.
  
  Discussed with: grehan@ and marcel@
  
  Revision  Changes    Path
  1.567     +1 -2      src/sys/amd64/amd64/pmap.c
  1.571     +1 -2      src/sys/i386/i386/pmap.c
  1.47      +0 -2      src/sys/sparc64/include/pmap.h
  1.78      +1 -0      src/sys/vm/pmap.h