Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756482AbZCFUZ0 (ORCPT ); Fri, 6 Mar 2009 15:25:26 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753795AbZCFUZL (ORCPT ); Fri, 6 Mar 2009 15:25:11 -0500 Received: from mx2.redhat.com ([66.187.237.31]:45449 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753773AbZCFUZJ (ORCPT ); Fri, 6 Mar 2009 15:25:09 -0500 Message-ID: <49B186A9.3030506@redhat.com> Date: Fri, 06 Mar 2009 15:25:13 -0500 From: Masami Hiramatsu User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Ingo Molnar CC: Mathieu Desnoyers , Andrew Morton , Nick Piggin , Steven Rostedt , Andi Kleen , Linux Kernel Mailing List , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" Subject: [PATCH -tip 5/4] Expands irq-off region in text_poke() References: <49B1428A.9050500@redhat.com> <49B14352.2040705@redhat.com> <20090306181356.GD14236@Krystal> <49B16C69.6060203@redhat.com> <20090306190828.GA28582@elte.hu> <20090306191517.GG14236@Krystal> <20090306192246.GF28582@elte.hu> In-Reply-To: <20090306192246.GF28582@elte.hu> X-Enigmail-Version: 0.95.7 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4590 Lines: 119 Ingo Molnar wrote: > * Mathieu Desnoyers wrote: > >> * Ingo Molnar (mingo@elte.hu) wrote: >>> * Masami Hiramatsu wrote: >>> >>>> @@ -523,14 +526,17 @@ 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); >>>> - local_irq_disable(); >>>> + local_irq_save(flags); >>>> + 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); >>>> memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); >>>> - local_irq_enable(); >>>> - vunmap(vaddr); >>>> + clear_fixmap(FIX_TEXT_POKE0); >>>> + if (pages[1]) >>>> + clear_fixmap(FIX_TEXT_POKE1); >>>> + local_flush_tlb(); >>>> + local_irq_restore(flags); >>>> sync_core(); >>> I'm not sure at all about this widening of the irq-atomic >>> section and the idea of allowing non-locked access on single-CPU >>> situations - we dont really want to micro-optimize any of this >>> on such a level, holding the text lock is a robust rule all code >>> should be listening to. (Creating locking assymetry always >>> inserts a certain amount of fragility - adding to an already >>> fragile concept here.) >>> >>> And note that there's no reason why text_poke could not be used >>> in stop_machine_run() - the stop_machine_run() handler must not >>> take the text_lock of course - but outside code calling >>> stop_machine_run() can do it and can hence serialize properly. >>> >>> Note that even if we did this then your v2 patch is not fully >>> correct: you need to move the sync_core() at the end of the >>> sequence inside the critical section too. (right now this is >>> mostly harmless because the INVLPG inside the clear_fixmap() >>> happens to be serializing so it has an implicit sync_core() >>> property - but nevertheless we better do this straight away to >>> not cause problems later down the line.) >>> >>> Ingo >> Agreed. The alternatives_smp_lock/alternatives_smp_unlock >> specific case does not bring us much if it has no perceivable >> performance impact. It's better to keep a standard interface >> and clear requirements. > > Note that i dont object to another aspect of this same change: > the fact that it makes the whole sequence more atomic and more > defensive [which is never bad of fragile interfaces]. > > I only got worried about the "lets use this without the text > lock" ideas. > > So if Masami-san sends a delta patch with a different changelog > and with the sync_core() bit moved inside the critical section, > i'll apply that too. OK, here is the delta patch. Expand irq-atomic region to cover fixmap using code and sync_core. Signed-off-by: Masami Hiramatsu Cc: Mathieu Desnoyers Cc: Ingo Molnar --- arch/x86/kernel/alternative.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) Index: linux-2.6-tip/arch/x86/kernel/alternative.c =================================================================== --- linux-2.6-tip.orig/arch/x86/kernel/alternative.c +++ linux-2.6-tip/arch/x86/kernel/alternative.c @@ -526,13 +526,12 @@ void *__kprobes text_poke(void *addr, co pages[1] = virt_to_page(addr + PAGE_SIZE); } BUG_ON(!pages[0]); + local_irq_save(flags); 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); clear_fixmap(FIX_TEXT_POKE0); if (pages[1]) clear_fixmap(FIX_TEXT_POKE1); @@ -540,6 +539,7 @@ void *__kprobes text_poke(void *addr, co sync_core(); /* Could also do a CLFLUSH here to speed up CPU recovery; but that causes hangs on some VIA CPUs. */ + local_irq_restore(flags); for (i = 0; i < len; i++) BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]); return addr; -- 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/