Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756846AbZCCQcT (ORCPT ); Tue, 3 Mar 2009 11:32:19 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753385AbZCCQcF (ORCPT ); Tue, 3 Mar 2009 11:32:05 -0500 Received: from mx2.redhat.com ([66.187.237.31]:43026 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753375AbZCCQcC (ORCPT ); Tue, 3 Mar 2009 11:32:02 -0500 Message-ID: <49AD5B55.10002@redhat.com> Date: Tue, 03 Mar 2009 11:31:17 -0500 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Ingo Molnar , Mathieu Desnoyers CC: Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , linux-kernel@vger.kernel.org, Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" , Steven Rostedt Subject: [PATCH] x86: make text_poke() atomic using fixmap References: <49A853CD.3020607@redhat.com> <49AC10E9.1090102@redhat.com> <20090302171914.GB21735@Krystal> <49AC5A87.7000604@redhat.com> <20090302222254.GA31962@elte.hu> <49AC63FA.70801@redhat.com> <20090302230915.GA11626@elte.hu> <49AC6DEA.2050304@redhat.com> <20090302234910.GA17956@elte.hu> <49AC7453.8020307@redhat.com> <20090303002214.GA4147@elte.hu> <49AC7A5F.7080009@redhat.com> In-Reply-To: <49AC7A5F.7080009@redhat.com> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5592 Lines: 161 Masami Hiramatsu wrote: > Ingo Molnar wrote: >> * Masami Hiramatsu wrote: >> >>> Ingo Molnar wrote: >>>> * Masami Hiramatsu wrote: >>>> >>>>> Ingo Molnar wrote: >>>>>>>> So perhaps another approach to (re-)consider would be to go back >>>>>>>> to atomic fixmaps here. It spends 3 slots but that's no big >>>>>>>> deal. >>>>>>> Oh, it's a good idea! fixmaps must make it simpler. >>>>>>> >>>>>>>> In exchange it will be conceptually simpler, and will also scale >>>>>>>> much better than a global spinlock. What do you think? >>>>>>> I think even if I use fixmaps, we have to use a spinlock to protect >>>>>>> the fixmap area from other threads... >>>>>> that's why i suggested to use an atomic-kmap, not a fixmap. >>>>> Even if the mapping is atomic, text_poke() has to protect pte >>>>> from other text_poke()s while changing code. >>>>> AFAIK, atomic-kmap itself doesn't ensure that, does it? >>>> Well, but text_poke() is not a serializing API to begin with. >>>> It's normally used in code patching sequences when we 'know' >>>> that there cannot be similar parallel activities. The kprobes >>>> usage of text_poke() looks unsafe - and that needs to be fixed. >>> Oh, kprobes already prohibited parallel arming/disarming >>> by using kprobe_mutex. :-) >> yeah, but still the API is somewhat unsafe. > > Yeah, kprobe_mutex protects text_poke from other kprobes, but > not from other text_poke() users... > >> In any case, you also answered your own question: >> >>>>> Even if the mapping is atomic, text_poke() has to protect pte >>>>> from other text_poke()s while changing code. >>>>> AFAIK, atomic-kmap itself doesn't ensure that, does it? >> kprobe_mutex does that. > > Anyway, text_edit_lock ensures that. > > By the way, I think set_fixmap/clear_fixmap seems simpler than > kmap_atomic() variant. Would you think improving kmap_atomic_prot() > is better? Hi Ingo, Here is the patch which uses fixmaps instead of vmap in text_poke(). This made the code much simpler than I thought :). Thanks, ---- Use fixmaps instead of vmap/vunmap in text_poke() for avoiding page allocation and delayed unmapping. At the result of above change, text_poke() becomes atomic and can be called from stop_machine() etc. Signed-off-by: Masami Hiramatsu Cc: Ingo Molnar Cc: Mathieu Desnoyers --- arch/x86/include/asm/fixmap_32.h | 2 ++ arch/x86/include/asm/fixmap_64.h | 2 ++ arch/x86/kernel/alternative.c | 18 ++++++++++++------ 3 files changed, 16 insertions(+), 6 deletions(-) Index: linux-2.6/arch/x86/include/asm/fixmap_32.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/fixmap_32.h +++ linux-2.6/arch/x86/include/asm/fixmap_32.h @@ -81,6 +81,8 @@ enum fixed_addresses { #ifdef CONFIG_PARAVIRT FIX_PARAVIRT_BOOTMAP, #endif + FIX_TEXT_POKE0, /* reserve 2 pages for text_poke() */ + FIX_TEXT_POKE1, __end_of_permanent_fixed_addresses, /* * 256 temporary boot-time mappings, used by early_ioremap(), Index: linux-2.6/arch/x86/include/asm/fixmap_64.h =================================================================== --- linux-2.6.orig/arch/x86/include/asm/fixmap_64.h +++ linux-2.6/arch/x86/include/asm/fixmap_64.h @@ -49,6 +49,8 @@ enum fixed_addresses { #ifdef CONFIG_PARAVIRT FIX_PARAVIRT_BOOTMAP, #endif + FIX_TEXT_POKE0, /* reserve 2 pages for text_poke() */ + FIX_TEXT_POKE1, __end_of_permanent_fixed_addresses, #ifdef CONFIG_ACPI FIX_ACPI_BEGIN, Index: linux-2.6/arch/x86/kernel/alternative.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/alternative.c +++ linux-2.6/arch/x86/kernel/alternative.c @@ -12,7 +12,9 @@ #include #include #include +#include #include +#include #define MAX_PATCH_LEN (255-1) @@ -495,12 +497,13 @@ void *text_poke_early(void *addr, const * It means the size must be writable atomically and the address must be aligned * in a way that permits an atomic write. It also makes sure we fit on a single * page. + * + * Note: Must be called under text_mutex. */ void *__kprobes text_poke(void *addr, const void *opcode, size_t len) { unsigned long flags; char *vaddr; - int nr_pages = 2; struct page *pages[2]; int i; @@ -513,14 +516,17 @@ void *__kprobes text_poke(void *addr, co pages[1] = virt_to_page(addr + PAGE_SIZE); } BUG_ON(!pages[0]); - if (!pages[1]) - nr_pages = 1; - vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL); - BUG_ON(!vaddr); + set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0])); + if (pages[1]) + set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1])); + vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0); local_irq_save(flags); memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); local_irq_restore(flags); - vunmap(vaddr); + clear_fixmap(FIX_TEXT_POKE0); + if (pages[1]) + clear_fixmap(FIX_TEXT_POKE1); + local_flush_tlb(); sync_core(); /* Could also do a CLFLUSH here to speed up CPU recovery; but that causes hangs on some VIA CPUs. */ -- Masami Hiramatsu Software Engineer Hitachi Computer Products (America) Inc. Software Solutions Division e-mail: mhiramat@redhat.com -- 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/