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Date: Thu, 23 Jul 2015 13:59:11 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Oleg Nesterov <oleg@redhat.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, Andy Lutomirski <luto@amacapital.net>,
        Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCHv2 2/6] x86, mpx: do not set ->vm_ops on mpx VMAs
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On Fri, 17 Jul 2015 14:53:09 +0300 "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com> wrote:

> MPX setups private anonymous mapping, but uses vma->vm_ops too.
> This can confuse core VM, as it relies on vm->vm_ops to distinguish
> file VMAs from anonymous.
> 
> As result we will get SIGBUS, because handle_pte_fault() thinks it's
> file VMA without vm_ops->fault and it doesn't know how to handle the
> situation properly.
> 
> Let's fix that by not setting ->vm_ops.
> 
> We don't really need ->vm_ops here: MPX VMA can be detected with VM_MPX
> flag. And vma_merge() will not merge MPX VMA with non-MPX VMA, because
> ->vm_flags won't match.
> 
> The only thing left is name of VMA. I'm not sure if it's part of ABI, or
> we can just drop it. The patch keep it by providing arch_vma_name() on x86.
> 
> Build tested only.

mpx.c has changed.

arch/x86/mm/mpx.c: In function 'try_unmap_single_bt':
arch/x86/mm/mpx.c:930: error: implicit declaration of function 'is_mpx_vma'

I'll drop this patch and see what happens.