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 15:21:56 +0300
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Dmitry Safonov <dsafonov@...tuozzo.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 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?

	Cyrill