From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755020AbYA3C2b (ORCPT ); Tue, 29 Jan 2008 21:28:31 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752017AbYA3C2X (ORCPT ); Tue, 29 Jan 2008 21:28:23 -0500 Received: from rv-out-0910.google.com ([209.85.198.187]:5945 "EHLO rv-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751893AbYA3C2W (ORCPT ); Tue, 29 Jan 2008 21:28:22 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=subject:from:to:cc:in-reply-to:references:content-type:date:message-id:mime-version:x-mailer:content-transfer-encoding; b=EMxCKgiukAemAAcIpjDEuWm8eobWXX5IdQ/bH6nL9vncAUvqMnfX4NFNemXD/o4UtymV2CpTVfcYcsl4NvRagrdHlwo8cz9TNDeM63Dqb68W/y/2wuHhvZmPP3WPRaSIiviZw23cnvi2UGBOJGLXHFmc92q4ad1DX/QNsQEU6Zc= Subject: Re: [PATCH] x86: Add a list for custom page fault handlers. From: Harvey Harrison To: Pekka Paalanen , Ingo Molnar Cc: linux-kernel@vger.kernel.org, Jan Beulich In-Reply-To: <20080127185238.4bcac54b@daedalus.pq.iki.fi> References: <20080127185238.4bcac54b@daedalus.pq.iki.fi> Content-Type: text/plain Date: Tue, 29 Jan 2008 18:28:22 -0800 Message-Id: <1201660102.8837.9.camel@brick> Mime-Version: 1.0 X-Mailer: Evolution 2.12.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Pekka Paalanen Provides kernel modules a way to register custom page fault handlers. On every page fault, except those handled in vmalloc_fault(), this will call a list of registered functions. The functions may handle the fault and force do_page_fault() to return immediately. This functionality is similar to the now removed page fault notifiers. Custom page fault handlers are used by debugging and reverse engineering tools. Mmio-trace is one such tool and a patch to add it into the tree will follow. The custom page fault handlers are called from the exact same points in do_page_fault() as the page fault notifiers were. Signed-off-by: Pekka Paalanen Signed-off-by: Harvey Harrison --- Ingo, ported Pekka's patch to current x86.git for review. I have not incorporated the RCU comments from Peter Zjistra, but I have folded some of the static functions into on handle_custom_pf function that will match the handle_kprobe_fault helper that will be ready for RC1. Harvey arch/x86/Kconfig.debug | 9 ++++++++ arch/x86/mm/fault.c | 51 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 60 insertions(+), 0 deletions(-) diff --git a/arch/x86/Kconfig.debug b/arch/x86/Kconfig.debug index 2e1e3af..9b44bc5 100644 --- a/arch/x86/Kconfig.debug +++ b/arch/x86/Kconfig.debug @@ -225,4 +225,13 @@ config CPA_DEBUG help Do change_page_attr self tests at boot. +config PAGE_FAULT_HANDLERS + bool "Custom page fault handlers" + depends on DEBUG_KERNEL + help + Allow the use of custom page fault handlers. A kernel module may + register a function that is called on every page fault not handled + for vmalloc. Custom handlers are used by some debugging and reverse + engineering tools. + endmenu diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c index e28cc52..c6c8164 100644 --- a/arch/x86/mm/fault.c +++ b/arch/x86/mm/fault.c @@ -49,6 +49,54 @@ #define PF_RSVD (1<<3) #define PF_INSTR (1<<4) +#ifdef CONFIG_PAGE_FAULT_HANDLERS +static HLIST_HEAD(pf_handlers); /* protected by RCU */ +static DEFINE_SPINLOCK(pf_handlers_writer); + +void register_page_fault_handler(struct pf_handler *new_pfh) +{ + spin_lock(&pf_handlers_writer); + hlist_add_head_rcu(&new_pfh->hlist, &pf_handlers); + spin_unlock(&pf_handlers_writer); +} +EXPORT_SYMBOL_GPL(register_page_fault_handler); + +void unregister_page_fault_handler(struct pf_handler *old_pfh) +{ + might_sleep(); + spin_lock(&pf_handlers_writer); + hlist_del_rcu(&old_pfh->hlist); + spin_unlock(&pf_handlers_writer); + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(unregister_page_fault_handler); +#endif + +/* returns non-zero if do_page_fault() should return */ +static int handle_custom_pf(struct pt_regs *regs, unsigned long error_code, + unsigned long address) +{ +#ifdef CONFIG_PAGE_FAULT_HANDLERS + int ret = 0; + struct pf_handler *cur; + struct hlist_node *ncur; + + if (hlist_empty(&pf_handlers)) + return 0; + + rcu_read_lock(); + hlist_for_each_entry_rcu(cur, ncur, &pf_handlers, hlist) { + ret = cur->handler(regs, error_code, address); + if (ret) + break; + } + rcu_read_unlock(); + return ret; +#else + return 0; +#endif +} + static inline int notify_page_fault(struct pt_regs *regs) { #ifdef CONFIG_KPROBES @@ -588,6 +636,9 @@ void __kprobes do_page_fault(struct pt_regs *regs, unsigned long error_code) if (notify_page_fault(regs)) return; + if (handle_custom_pf(regs, error_code, address)) + return; + /* * We fault-in kernel-space virtual memory on-demand. The * 'reference' page table is init_mm.pgd. -- 1.5.4.rc4.1142.gf5a97