Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1751172AbbD3LuJ (ORCPT <rfc822;w@1wt.eu>);
	Thu, 30 Apr 2015 07:50:09 -0400
Received: from mail-lb0-f178.google.com ([209.85.217.178]:36488 "EHLO
	mail-lb0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750923AbbD3LuG (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Thu, 30 Apr 2015 07:50:06 -0400
MIME-Version: 1.0
In-Reply-To: <CA+55aFzW52u-LahoBA5kDs47rgeTGU_KF_GUrx+XSUDzeQD3=g@mail.gmail.com>
References: <CAEVpBa+_RyACkhODZrRvQLs80iy0sqpdrd0AaP_-tgnX3Y9yNQ@mail.gmail.com>
	<CAL82V5P-6_3kKfkgBuv1WMSu5xQ-0mUs7pHXegyPAzgroTgLtA@mail.gmail.com>
	<CAEVpBa+vjfR8p_fJQPXyrQCMYJOocQpTHmkTYmj7nOpGcce=Pg@mail.gmail.com>
	<CAEVpBa+DPbhZeRsA=+Jnn7f1BqVZm9SU=ABjy6bAHbbMi_yn+g@mail.gmail.com>
	<20150429193622.GA11892@node.dhcp.inet.fi>
	<CA+55aFx67hC3RxvAXYXWp=6mN_cfyMVqh_TDJVEqiV17o8+PtA@mail.gmail.com>
	<CALYGNiN6kU5xgEAfbs4VVXsVKmMN+uCStrQoLh6gFCzBxJfy+A@mail.gmail.com>
	<CA+55aFzW52u-LahoBA5kDs47rgeTGU_KF_GUrx+XSUDzeQD3=g@mail.gmail.com>
Date: Thu, 30 Apr 2015 12:50:04 +0100
Message-ID: <CAEVpBaJ3z12p6qfpisu5Fy2sPQhDBvbHsE-PAGNRM2A3P98Y3Q@mail.gmail.com>
Subject: Re: Regression: Requiring CAP_SYS_ADMIN for /proc/<pid>/pagemap
 causes application-level breakage
From: Mark Williamson <mwilliamson@undo-software.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Konstantin Khlebnikov <koct9i@gmail.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
        Mark Seaborn <mseaborn@chromium.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Pavel Emelyanov <xemul@parallels.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Andy Lutomirski <luto@amacapital.net>,
        Linux API <linux-api@vger.kernel.org>,
        Finn Grimwood <fgrimwood@undo-software.com>,
        Daniel James <djames@undo-software.com>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 1636
Lines: 37

On Wed, Apr 29, 2015 at 10:02 PM, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
> On Wed, Apr 29, 2015 at 1:44 PM, Konstantin Khlebnikov <koct9i@gmail.com> wrote:
>>
>> This's no longer true. After recent fixes for "anon_vma endless growing" new vma
>> might reuse old anon_vma from grandparent vma.
>
> Oh well. I guess that was too simple.
>
> If Mark is ok with the rule that "it's not reliably if you have two
> nested forks" (ie it only works if you exec for every fork you do), it
> should still work, right? It sounds like Mark doesn't necessarily need
> to handle the *generic* case.

Yes, it sounds like that should be OK for us.  Our usecase is pretty
restricted, so we're a long way off requiring a generic solution.

Our code will always fork() a fresh child in which to monitor memory
changes.  We run the operations we're interested in, use pagemap to
figure out "what changed" (by comparing whether the pagemap_entry_t
values are different from their parent) and then throw away the child
process.

Currently our code does an entry-by-entry compare of pagemap, so
anything that exposes writes as a change to values in there would
allow us to run unmodified.  That would be really nice.  That said, I
think we'd still be OK to modify our own code too if we can find a
solution that would continue to function on older kernel releases,
-stable trees, etc.

Thanks,
Mark
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/