linux-kernel - Re: [PATCH 1/2] x86/arch_prctl: add ARCH_SET_{COMPAT,NATIVE} to change compatible mode

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Date:	Thu, 7 Apr 2016 15:35:10 +0300
From:	Dmitry Safonov <dsafonov@...tuozzo.com>
To:	Cyrill Gorcunov <gorcunov@...il.com>,
	Andy Lutomirski <luto@...capital.net>
CC:	Shuah Khan <shuahkh@....samsung.com>,
	"H. Peter Anvin" <hpa@...or.com>, <0x7f454c46@...il.com>,
	<khorenko@...tuozzo.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>, <xemul@...tuozzo.com>,
	<linux-kselftest@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	X86 ML <x86@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>
Subject: Re: [PATCH 1/2] x86/arch_prctl: add ARCH_SET_{COMPAT,NATIVE} to
 change compatible mode

On 04/07/2016 03:21 PM, Cyrill Gorcunov wrote:
> On Thu, Apr 07, 2016 at 03:11:24PM +0300, Dmitry Safonov wrote:
>> On 04/06/2016 09:04 PM, Andy Lutomirski wrote:
>>> [cc Dave Hansen for MPX]
>>>
>> Will add x32 support for v2.
>>> I think that you should separate vdso remapping from "personality".
>>> vdso remapping should be available even on native 32-bit builds, which
>>> means that either you can't use arch_prctl for it or you'll have to
>>> wire up arch_prctl as a 32-bit syscall.
>> I cant say, I got your point. Do you mean by vdso remapping
>> mremap for vdso/vvar pages? I think, it should work now.
>> I did remapping for vdso as blob for native x86_64 task differs
>> to compatible task. So it's just changing blobs, address value
>> is there for convenience - I may omit it and just remap
>> different vdso blob at the same place where was previous vdso.
>> I'm not sure, why do we need possibility to map 64-bit vdso blob
>> on native 32-bit builds?
> First of all, thanks a huge for all your comments, Andy!
> Dima, I'm not seeing in patch, don't you have to take
> mm::mmap_sem when walking over VMAs?
I was sure I did, but have missed it, well.
Thanks!
>
> 	Cyrill


-- 
Regards,
Dmitry Safonov