• Linus Torvalds's avatar
    mm: do not initialize TLB stack vma's with vma_init() · 8b11ec1b
    Linus Torvalds authored
    Commit 2c4541e2 ("mm: use vma_init() to initialize VMAs on stack and
    data segments") tried to initialize various left-over ad-hoc vma's
    "properly", but actually made things worse for the temporary vma's used
    for TLB flushing.
    vma_init() doesn't actually initialize all of the vma, just a few
    fields, so doing something like
       -       struct vm_area_struct vma = { .vm_mm = tlb->mm, };
       +       struct vm_area_struct vma;
       +       vma_init(&vma, tlb->mm);
    was actually very bad: instead of having a nicely initialized vma with
    every field but "vm_mm" zeroed, you'd have an entirely uninitialized vma
    with only a couple of fields initialized.  And they weren't even fields
    that the code in question mostly cared about.
    The flush_tlb_range() function takes a "struct vma" rather than a
    "struct mm_struct", because a few architectures actually care about what
    kind of range it is - being able to only do an ITLB flush if it's a
    range that doesn't have data accesses enabled, for example.  And all the
    normal users already have the vma for doing the range invalidation.
    But a few people want to call flush_tlb_range() with a range they just
    made up, so they also end up using a made-up vma.  x86 just has a
    special "flush_tlb_mm_range()" function for this, but other
    architectures (arm and ia64) do the "use fake vma" thing instead, and
    thus got caught up in the vma_init() changes.
    At the same time, the TLB flushing code really doesn't care about most
    other fields in the vma, so vma_init() is just unnecessary and
    This fixes things by having an explicit "this is just an initializer for
    the TLB flush" initializer macro, which is used by the arm/arm64/ia64
    people who mis-use this interface with just a dummy vma.
    Fixes: 2c4541e2 ("mm: use vma_init() to initialize VMAs on stack and data segments")
    Cc: Dmitry Vyukov <dvyukov@google.com>
    Cc: Oleg Nesterov <oleg@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: Kirill Shutemov <kirill.shutemov@linux.intel.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Hugh Dickins <hughd@google.com>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
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