From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932983Ab2HVPWu (ORCPT ); Wed, 22 Aug 2012 11:22:50 -0400 Received: from smtp.eu.citrix.com ([62.200.22.115]:52454 "EHLO SMTP.EU.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932914Ab2HVPWU (ORCPT ); Wed, 22 Aug 2012 11:22:20 -0400 X-IronPort-AV: E=Sophos;i="4.77,808,1336348800"; d="scan'208";a="14130223" From: Attilio Rao To: , , , , , , CC: Attilio Rao Subject: [PATCH v4 2/2] XEN: Document the semantic of x86_init.mapping.pagetable_reserve Date: Wed, 22 Aug 2012 16:08:42 +0100 Message-ID: <1345648122-11935-3-git-send-email-attilio.rao@citrix.com> X-Mailer: git-send-email 1.7.2.5 In-Reply-To: <1345648122-11935-1-git-send-email-attilio.rao@citrix.com> References: <1345648122-11935-1-git-send-email-attilio.rao@citrix.com> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org The informations added on the hook are: - Native behaviour - Xen specific behaviour - Logic behind the Xen specific behaviour - setup function semantic Even if in general it would be a good idea to separate implementation from semantic, in this case it is beneficial to give a little bit of context on the implementation in order to favourably understand the semantic. Signed-off-by: Attilio Rao Reviewed-by: Konrad Rzeszutek Wilk Acked-by: Stefano Stabellini --- arch/x86/include/asm/x86_init.h | 19 +++++++++++++++++-- 1 files changed, 17 insertions(+), 2 deletions(-) diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h index 38155f6..b22093c 100644 --- a/arch/x86/include/asm/x86_init.h +++ b/arch/x86/include/asm/x86_init.h @@ -72,8 +72,23 @@ struct x86_init_oem { * struct x86_init_mapping - platform specific initial kernel pagetable setup * @pagetable_reserve: reserve a range of addresses for kernel pagetable usage * - * For more details on the purpose of this hook, look in - * init_memory_mapping and the commit that added it. + * It does reserve a range of pages, to be used as pagetable pages. + * The start and end parameters are expected to be contained in the + * [pgt_buf_start, pgt_buf_top] range. + * The native implementation reserves the pages via the memblock_reserve() + * interface. + * The Xen implementation, besides reserving the range via memblock_reserve(), + * also sets RW the remaining pages contained in the ranges + * [pgt_buf_start, start) and [end, pgt_buf_top). + * This is needed because the range [pgt_buf_start, pgt_buf_top] was + * previously mapped read-only by xen_set_pte_init: when running + * on Xen all the pagetable pages need to be mapped read-only in order to + * avoid protection faults from the hypervisor. However, once the correct + * amount of pages is reserved for the pagetables, all the others contained + * in the range must be set to RW so that they can be correctly recycled by + * the VM subsystem. + * This operation is meant to be performed only during init_memory_mapping(), + * just after space for the kernel direct mapping tables is found. */ struct x86_init_mapping { void (*pagetable_reserve)(u64 start, u64 end); -- 1.7.2.5