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    SubjectRe: [RFC PATCH] mm, oom_reaper: gather each vma to prevent leaking TLB entry
    On Mon, Nov 6, 2017 at 11:36 AM, Wang Nan <wangnan0@huawei.com> wrote:
    > tlb_gather_mmu(&tlb, mm, 0, -1) means gathering all virtual memory space.
    > In this case, tlb->fullmm is true. Some archs like arm64 doesn't flush
    > TLB when tlb->fullmm is true:
    >
    > commit 5a7862e83000 ("arm64: tlbflush: avoid flushing when fullmm == 1").
    >

    CC'ed Will Deacon.

    > Which makes leaking of tlb entries. For example, when oom_reaper
    > selects a task and reaps its virtual memory space, another thread
    > in this task group may still running on another core and access
    > these already freed memory through tlb entries.
    >
    > This patch gather each vma instead of gathering full vm space,
    > tlb->fullmm is not true. The behavior of oom reaper become similar
    > to munmapping before do_exit, which should be safe for all archs.
    >
    > Signed-off-by: Wang Nan <wangnan0@huawei.com>
    > Cc: Bob Liu <liubo95@huawei.com>
    > Cc: Michal Hocko <mhocko@suse.com>
    > Cc: Andrew Morton <akpm@linux-foundation.org>
    > Cc: Michal Hocko <mhocko@suse.com>
    > Cc: David Rientjes <rientjes@google.com>
    > Cc: Ingo Molnar <mingo@kernel.org>
    > Cc: Roman Gushchin <guro@fb.com>
    > Cc: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
    > Cc: Andrea Arcangeli <aarcange@redhat.com>
    > ---
    > mm/oom_kill.c | 7 ++++---
    > 1 file changed, 4 insertions(+), 3 deletions(-)
    >
    > diff --git a/mm/oom_kill.c b/mm/oom_kill.c
    > index dee0f75..18c5b35 100644
    > --- a/mm/oom_kill.c
    > +++ b/mm/oom_kill.c
    > @@ -532,7 +532,6 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
    > */
    > set_bit(MMF_UNSTABLE, &mm->flags);
    >
    > - tlb_gather_mmu(&tlb, mm, 0, -1);
    > for (vma = mm->mmap ; vma; vma = vma->vm_next) {
    > if (!can_madv_dontneed_vma(vma))
    > continue;
    > @@ -547,11 +546,13 @@ static bool __oom_reap_task_mm(struct task_struct *tsk, struct mm_struct *mm)
    > * we do not want to block exit_mmap by keeping mm ref
    > * count elevated without a good reason.
    > */
    > - if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED))
    > + if (vma_is_anonymous(vma) || !(vma->vm_flags & VM_SHARED)) {
    > + tlb_gather_mmu(&tlb, mm, vma->vm_start, vma->vm_end);
    > unmap_page_range(&tlb, vma, vma->vm_start, vma->vm_end,
    > NULL);
    > + tlb_finish_mmu(&tlb, vma->vm_start, vma->vm_end);
    > + }
    > }
    > - tlb_finish_mmu(&tlb, 0, -1);
    > pr_info("oom_reaper: reaped process %d (%s), now anon-rss:%lukB, file-rss:%lukB, shmem-rss:%lukB\n",
    > task_pid_nr(tsk), tsk->comm,
    > K(get_mm_counter(mm, MM_ANONPAGES)),

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