Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756252Ab1BCLXi (ORCPT ); Thu, 3 Feb 2011 06:23:38 -0500 Received: from smtp.ctxuk.citrix.com ([62.200.22.115]:46527 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756213Ab1BCLXh (ORCPT ); Thu, 3 Feb 2011 06:23:37 -0500 X-IronPort-AV: E=Sophos;i="4.60,418,1291593600"; d="scan'208";a="4129596" Date: Thu, 3 Feb 2011 11:25:19 +0000 From: Stefano Stabellini X-X-Sender: sstabellini@kaball-desktop To: "H. Peter Anvin" CC: Stefano Stabellini , "linux-kernel@vger.kernel.org" , "tglx@linutronix.de" , "x86@kernel.org" , Konrad Rzeszutek Wilk , Jeremy Fitzhardinge , Jan Beulich Subject: Re: [PATCH] x86/mm/init: respect memblock reserved regions when destroying mappings In-Reply-To: <4D4A3782.3050702@zytor.com> Message-ID: References: <4D4A3782.3050702@zytor.com> User-Agent: Alpine 2.00 (DEB 1167 2008-08-23) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1987 Lines: 46 On Thu, 3 Feb 2011, H. Peter Anvin wrote: > On 01/31/2011 07:18 AM, Stefano Stabellini wrote: > > x86/mm/init: respect memblock reserved regions when destroying mappings > > > > In init_memory_mapping we are destroying all the mappings between > > _brk_end and _end, no matter if some memory areas in that range have > > been reserved using memblock_x86_reserve_range. > > Besides if _end is not pmd aligned we might destroy the > > mappings for valid memory between _end and the following pmd. > > > > In order to avoid this problem, before clearing any pmds we check if the > > corresponding memory area has been reserved and we only destroy the > > mapping if it hasn't. > > > > We found this problem because under Xen we have a valid mapping at _end, > > and if _end is not pmd aligned the current code destroys the initial > > part of it. > > > > In practice this fix does not have any impact on native. > > > > Signed-off-by: Stefano Stabellini > > How on Earth would you end up with a reserved region *inside the BRK*? I think in practice you cannot, but you can have reserved regions at _end, that is the main problem I am trying to solve. If we have a reserved region at _end and _end is not PMD aligned, then we have a problem. I thought that checking for reserved regions before destroying the mapping would be a decent solution (because it wouldn't affect the normal case); so I ended up checking between _brk_end and _end too. Other alternative solutions I thought about but that I discarded because they also affect the normal case are: - never destroy mappings that could go over _end; - always PMD align _end. If none of the above are acceptable, I welcome other suggestions :-) -- 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/