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Date:   Fri, 12 Apr 2019 20:19:30 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Nadav Amit <namit@vmware.com>
Cc:     kernel test robot <lkp@intel.com>, LKP <lkp@01.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Will Deacon <will.deacon@arm.com>,
        Andy Lutomirski <luto@kernel.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>
Subject: Re: 1808d65b55 ("asm-generic/tlb: Remove arch_tlb*_mmu()"):  BUG:
 KASAN: stack-out-of-bounds in __change_page_attr_set_clr
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On Fri, Apr 12, 2019 at 03:11:22PM +0000, Nadav Amit wrote:
> > On Apr 12, 2019, at 4:17 AM, Peter Zijlstra <peterz@infradead.org> wrote:

> > To clarify, 'that' is Nadav's patch:
> > 
> >  515ab7c41306 ("x86/mm: Align TLB invalidation info")
> > 
> > which turns out to be the real problem.
> 
> Sorry for that. I still think it should be aligned, especially with all the
> effort the Intel puts around to avoid bus-locking on unaligned atomic
> operations.

No atomics anywhere in sight, so that's not a concern.

> So the right solution seems to me as putting this data structure off stack.
> It would prevent flush_tlb_mm_range() from being reentrant, so we can keep a
> few entries for this matter and atomically increase the entry number every
> time we enter flush_tlb_mm_range().
> 
> But my question is - should flush_tlb_mm_range() be reentrant, or can we
> assume no TLB shootdowns are initiated in interrupt handlers and #MC
> handlers?

There _should_ not be, but then don't look at those XPFO patches that
were posted (they're broken anyway).