linux-kernel - Re: [PATCHv2 2/6] x86, mpx: do not set ->vm

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Message-Id: <20150723135911.af81b6a685f5b779ca66f3c3@linux-foundation.org>
Date:	Thu, 23 Jul 2015 13:59:11 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:	Oleg Nesterov <oleg@...hat.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org,
	Andy Lutomirski <luto@...capital.net>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCHv2 2/6] x86, mpx: do not set ->vm_ops on mpx VMAs

On Fri, 17 Jul 2015 14:53:09 +0300 "Kirill A. Shutemov" <kirill.shutemov@...ux.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.
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