Messages in this thread | | | Date | Thu, 3 Oct 2013 08:34:16 -0700 | Subject | Re: [RFC] perf: mmap2 not covering VM_CLONE regions | From | Kees Cook <> |
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On Thu, Oct 3, 2013 at 2:13 AM, Stephane Eranian <eranian@google.com> wrote: > On Thu, Oct 3, 2013 at 11:03 AM, Peter Zijlstra <peterz@infradead.org> wrote: >> On Thu, Oct 03, 2013 at 10:55:28AM +0200, Stephane Eranian wrote: >>> I don't know the MM code but I assume that that vm_mm struct is >>> allocated dynamically >>> and maybe you already grabbing a lock while doing this. Could we >>> leverage that lock >>> to increment a global generation number? >> >> Sure; something like so.. I just don't like global state nor adding to >> mm_struct for just this. >> > I understand, I don't like global state either. I see you already > have uprobes state in there. Thus to me, the perf situation is > not much worse in terms of usefulness (frequency of use). > > Thanks. > >> --- >> include/linux/mm_types.h | 1 + >> kernel/fork.c | 6 ++++++ >> 2 files changed, 7 insertions(+) >> >> diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h >> index d9851eeb6e1d..3877b1e72a5b 100644 >> --- a/include/linux/mm_types.h >> +++ b/include/linux/mm_types.h >> @@ -436,6 +436,7 @@ struct mm_struct { >> int first_nid; >> #endif >> struct uprobes_state uprobes_state; >> + u64 mm_id; >> }; >> >> /* first nid will either be a valid NID or one of these values */ >> diff --git a/kernel/fork.c b/kernel/fork.c >> index 086fe73ad6bd..b315f6227629 100644 >> --- a/kernel/fork.c >> +++ b/kernel/fork.c >> @@ -523,6 +523,8 @@ static void mm_init_aio(struct mm_struct *mm) >> #endif >> } >> >> +static u64 global_mm_id; >> + >> static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p) >> { >> atomic_set(&mm->mm_users, 1); >> @@ -537,6 +539,7 @@ static struct mm_struct *mm_init(struct mm_struct *mm, struct task_struct *p) >> spin_lock_init(&mm->page_table_lock); >> mm_init_aio(mm); >> mm_init_owner(mm, p); >> + mm->mm_id = 0; >> >> if (likely(!mm_alloc_pgd(mm))) { >> mm->def_flags = 0; >> @@ -1422,6 +1425,9 @@ static struct task_struct *copy_process(unsigned long clone_flags, >> */ >> write_lock_irq(&tasklist_lock); >> >> + if (p->mm && !p->mm->mm_id) >> + p->mm->mm_id = ++global_mm_id; >> + >> /* CLONE_PARENT re-uses the old parent */ >> if (clone_flags & (CLONE_PARENT|CLONE_THREAD)) { >> p->real_parent = current->real_parent;
FWIW, I like this approach.
-Kees
-- Kees Cook Chrome OS Security
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