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    Subject[PATCH 4.9 16/75] x86/mm: Make flush_tlb_mm_range() more predictable
    Date
    4.9-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Andy Lutomirski <luto@kernel.org>

    commit ce27374fabf553153c3f53efcaa9bfab9216bd8c upstream.

    I'm about to rewrite the function almost completely, but first I
    want to get a functional change out of the way. Currently, if
    flush_tlb_mm_range() does not flush the local TLB at all, it will
    never do individual page flushes on remote CPUs. This seems to be
    an accident, and preserving it will be awkward. Let's change it
    first so that any regressions in the rewrite will be easier to
    bisect and so that the rewrite can attempt to change no visible
    behavior at all.

    The fix is simple: we can simply avoid short-circuiting the
    calculation of base_pages_to_flush.

    As a side effect, this also eliminates a potential corner case: if
    tlb_single_page_flush_ceiling == TLB_FLUSH_ALL, flush_tlb_mm_range()
    could have ended up flushing the entire address space one page at a
    time.

    Signed-off-by: Andy Lutomirski <luto@kernel.org>
    Acked-by: Dave Hansen <dave.hansen@intel.com>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Borislav Petkov <bp@alien8.de>
    Cc: Brian Gerst <brgerst@gmail.com>
    Cc: Denys Vlasenko <dvlasenk@redhat.com>
    Cc: H. Peter Anvin <hpa@zytor.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Michal Hocko <mhocko@suse.com>
    Cc: Nadav Amit <namit@vmware.com>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Rik van Riel <riel@redhat.com>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Link: http://lkml.kernel.org/r/4b29b771d9975aad7154c314534fec235618175a.1492844372.git.luto@kernel.org
    Signed-off-by: Ingo Molnar <mingo@kernel.org>
    Cc: Hugh Dickins <hughd@google.com>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/mm/tlb.c | 12 +++++++-----
    1 file changed, 7 insertions(+), 5 deletions(-)

    --- a/arch/x86/mm/tlb.c
    +++ b/arch/x86/mm/tlb.c
    @@ -307,6 +307,12 @@ void flush_tlb_mm_range(struct mm_struct
    unsigned long base_pages_to_flush = TLB_FLUSH_ALL;

    preempt_disable();
    +
    + if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
    + base_pages_to_flush = (end - start) >> PAGE_SHIFT;
    + if (base_pages_to_flush > tlb_single_page_flush_ceiling)
    + base_pages_to_flush = TLB_FLUSH_ALL;
    +
    if (current->active_mm != mm) {
    /* Synchronize with switch_mm. */
    smp_mb();
    @@ -323,15 +329,11 @@ void flush_tlb_mm_range(struct mm_struct
    goto out;
    }

    - if ((end != TLB_FLUSH_ALL) && !(vmflag & VM_HUGETLB))
    - base_pages_to_flush = (end - start) >> PAGE_SHIFT;
    -
    /*
    * Both branches below are implicit full barriers (MOV to CR or
    * INVLPG) that synchronize with switch_mm.
    */
    - if (base_pages_to_flush > tlb_single_page_flush_ceiling) {
    - base_pages_to_flush = TLB_FLUSH_ALL;
    + if (base_pages_to_flush == TLB_FLUSH_ALL) {
    count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
    local_flush_tlb();
    } else {

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