• Jeff Dike's avatar
    uml: cover stubs with a VMA · 3963333f
    Jeff Dike authored
    Give the stubs a VMA.  This allows the removal of a truly nasty kludge to make
    sure that mm->nr_ptes was correct in exit_mmap.  The underlying problem was
    always that the stubs, which have ptes, and thus allocated a page table,
    weren't covered by a VMA.
    
    This patch fixes that by using install_special_mapping in arch_dup_mmap and
    activate_context to create the VMA.  The stubs have to be moved, since
    shift_arg_pages seems to assume that the stack is the only VMA present at that
    point during exec, and uses vma_adjust to fiddle its VMA.  However, that
    extends the stub VMA by the amount removed from the stack VMA.
    
    To avoid this problem, the stubs were moved to a different fixed location at
    the start of the address space.
    
    The init_stub_pte calls were moved from init_new_context to arch_dup_mmap
    because I was occasionally seeing arch_dup_mmap not being called, causing
    exit_mmap to die.  Rather than figure out what was really happening, I decided
    it was cleaner to just move the calls so that there's no doubt that both the
    pte and VMA creation happen, no matter what.  arch_exit_mmap is used to clear
    the stub ptes at exit time.
    
    The STUB_* constants in as-layout.h no longer depend on UM_TASK_SIZE, that
    that definition is removed, along with the comments complaining about gcc.
    
    Because the stubs are no longer at the top of the address space, some care is
    needed while flushing TLBs.  update_pte_range checks for addresses in the stub
    range and skips them.  flush_thread now issues two unmaps, one for the range
    before STUB_START and one for the range after STUB_END.
    Signed-off-by: default avatarJeff Dike <jdike@linux.intel.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    3963333f
as-layout.h 1.58 KB