From: Peter Zijlstra <peterz@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-kernel@vger.kernel.org, luto@amacapital.net,
axboe@kernel.dk, keescook@chromium.org,
torvalds@linux-foundation.org, jannh@google.com, will@kernel.org
Subject: [PATCH v2] mm: Fix use_mm() vs TLB invalidate
Date: Wed, 26 Feb 2020 14:21:33 +0100 [thread overview]
Message-ID: <20200226132133.GM14946@hirez.programming.kicks-ass.net> (raw)
For SMP systems using IPI based TLB invalidation, looking at
current->active_mm is entirely reasonable. This then presents the
following race condition:
CPU0 CPU1
flush_tlb_mm(mm) use_mm(mm)
<send-IPI>
tsk->active_mm = mm;
<IPI>
if (tsk->active_mm == mm)
// flush TLBs
</IPI>
switch_mm(old_mm,mm,tsk);
Where it is possible the IPI flushed the TLBs for @old_mm, not @mm,
because the IPI lands before we actually switched.
Avoid this by disabling IRQs across changing ->active_mm and
switch_mm().
[ There are all sorts of reasons this might be harmless for various
architecture specific reasons, but best not leave the door open at
all. ]
Cc: stable@kernel.org
Reported-by: Andy Lutomirski <luto@amacapital.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
v2 now with WARN_ON_ONCE
mmu_context.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)
Index: linux-2.6/mm/mmu_context.c
===================================================================
--- linux-2.6.orig/mm/mmu_context.c
+++ linux-2.6/mm/mmu_context.c
@@ -24,14 +24,19 @@ void use_mm(struct mm_struct *mm)
struct mm_struct *active_mm;
struct task_struct *tsk = current;
+ WARN_ON(!(tsk->flags & PF_KTHREAD));
+ WARN_ON(tsk->mm != NULL);
+
task_lock(tsk);
+ local_irq_disable();
active_mm = tsk->active_mm;
if (active_mm != mm) {
mmgrab(mm);
tsk->active_mm = mm;
}
tsk->mm = mm;
- switch_mm(active_mm, mm, tsk);
+ switch_mm_irqs_off(active_mm, mm, tsk);
+ local_irq_enable();
task_unlock(tsk);
#ifdef finish_arch_post_lock_switch
finish_arch_post_lock_switch();
@@ -54,11 +59,15 @@ void unuse_mm(struct mm_struct *mm)
{
struct task_struct *tsk = current;
+ WARN_ON(!(tsk->flags & PF_KTHREAD));
+
task_lock(tsk);
sync_mm_rss(mm);
+ local_irq_disable();
tsk->mm = NULL;
/* active_mm is still 'mm' */
enter_lazy_tlb(mm, tsk);
+ local_irq_enable();
task_unlock(tsk);
}
EXPORT_SYMBOL_GPL(unuse_mm);
next reply other threads:[~2020-02-26 13:21 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 13:21 Peter Zijlstra [this message]
2020-02-26 14:13 ` [PATCH v2] mm: Fix use_mm() vs TLB invalidate Jens Axboe
2020-02-26 21:36 ` Kees Cook
2020-03-03 10:01 ` Peter Zijlstra
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