From mboxrd@z Thu Jan 1 00:00:00 1970 From: Attilio Rao Subject: [PATCH 2/2] Document the semantic of the pagetable_reserve PVOP Date: Fri, 10 Aug 2012 15:17:07 +0100 Message-ID: <1344608227-30910-3-git-send-email-attilio.rao@citrix.com> References: <1344608227-30910-1-git-send-email-attilio.rao@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1344608227-30910-1-git-send-email-attilio.rao@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: xen-devel@lists.xen.org, Stefano Stabellini , Konrad Rzeszutek Wilk Cc: Attilio Rao List-Id: xen-devel@lists.xenproject.org The informations added on the hook are: - Native behaviour - Xen specific behaviour - Logic behind the Xen specific behaviour - PVOP semantic Signed-off-by: Attilio Rao --- 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