From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758367AbZB0SHj (ORCPT ); Fri, 27 Feb 2009 13:07:39 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753196AbZB0SHa (ORCPT ); Fri, 27 Feb 2009 13:07:30 -0500 Received: from tomts16.bellnexxia.net ([209.226.175.4]:51175 "EHLO tomts16-srv.bellnexxia.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752460AbZB0SH3 (ORCPT ); Fri, 27 Feb 2009 13:07:29 -0500 X-IronPort-Anti-Spam-Filtered: true X-IronPort-Anti-Spam-Result: AsIEAGe5p0lMQWWY/2dsb2JhbACBWdVZhBQG Date: Fri, 27 Feb 2009 13:07:24 -0500 From: Mathieu Desnoyers To: Masami Hiramatsu Cc: Steven Rostedt , Andi Kleen , linux-kernel@vger.kernel.org, Ingo Molnar , Andrew Morton , Thomas Gleixner , Peter Zijlstra , Frederic Weisbecker , Linus Torvalds , Arjan van de Ven , Rusty Russell , "H. Peter Anvin" , Steven Rostedt Subject: Re: [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions Message-ID: <20090227180724.GA17947@Krystal> References: <20090223045357.GA9158@Krystal> <20090223154258.GB28727@Krystal> <20090223161312.GA30279@Krystal> <20090223173108.GB1441@Krystal> <49A82851.5080707@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Content-Disposition: inline In-Reply-To: <49A82851.5080707@redhat.com> X-Editor: vi X-Info: http://krystal.dyndns.org:8080 X-Operating-System: Linux/2.6.21.3-grsec (i686) X-Uptime: 13:01:49 up 6 days, 9:35, 3 users, load average: 0.37, 0.47, 0.38 User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Masami Hiramatsu (mhiramat@redhat.com) wrote: > Steven Rostedt wrote: > > On Mon, 23 Feb 2009, Mathieu Desnoyers wrote: > >>> Hmm, lets see. I simply set a bit in the PTE mappings. There's not many, > >>> since a lot are 2M pages, for x86_64. Call stop_machine, and now I can > >>> modify 1 or 20,000 locations. Set the PTE bit back. Note, the changing of > >>> the bits are only done when CONFIG_DEBUG_RODATA is set. > >>> > >>> text_poke requires allocating a page. Map the page into memory. Set up a > >>> break point. > >> text_poke does not _require_ a break point. text_poke can work with > >> stop_machine. > > > > It can? Doesn't text_poke require allocating pages? The code called by > > stop_machine is all atomic. vmap does not give an option to allocate with > > GFP_ATOMIC. > > Hi, > > With my patch, text_poke() never allocate pages any more :) > > BTW, IMHO, both of your methods are useful and have trade-off. > > ftrace wants to change massive amount of code at once. If we do > that with text_poke(), we have to map/unmap pages each time and > it will take a long time -- might be longer than one stop_machine_run(). > > On the other hand, text_poke() user like as kprobes and tracepoints, > just want to change a few amount of code at once, and it will be > added/removed incrementally. If we do that with stop_machine_run(), > we'll be annoyed by frequent machine stops.(Moreover, kprobes uses > breakpoint, so it doesn't need stop_machine_run()) > Hi Masami, Is this text_poke version executable in atomic context ? If yes, then that would be good to add a comment saying it. Please see below for comments. > > Thank you, > [...] > Use map_vm_area() instead of vmap() in text_poke() for avoiding page allocation > and delayed unmapping. > > Signed-off-by: Masami Hiramatsu > --- > arch/x86/include/asm/alternative.h | 1 + > arch/x86/kernel/alternative.c | 25 ++++++++++++++++++++----- > init/main.c | 3 +++ > 3 files changed, 24 insertions(+), 5 deletions(-) > > Index: linux-2.6/arch/x86/include/asm/alternative.h > =================================================================== > --- linux-2.6.orig/arch/x86/include/asm/alternative.h > +++ linux-2.6/arch/x86/include/asm/alternative.h > @@ -177,6 +177,7 @@ extern void add_nops(void *insns, unsign > * The _early version expects the memory to already be RW. > */ > > +extern void text_poke_init(void); > extern void *text_poke(void *addr, const void *opcode, size_t len); > extern void *text_poke_early(void *addr, const void *opcode, size_t len); > > 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 > @@ -485,6 +485,16 @@ void *text_poke_early(void *addr, const > return addr; > } > > +static struct vm_struct *text_poke_area[2]; > +static DEFINE_SPINLOCK(text_poke_lock); > + > +void __init text_poke_init(void) > +{ > + text_poke_area[0] = get_vm_area(PAGE_SIZE, VM_ALLOC); > + text_poke_area[1] = get_vm_area(2 * PAGE_SIZE, VM_ALLOC); Why is this text_poke_area[1] 2 * PAGE_SIZE in size ? I would have thought that text_poke_area[0] would be PAGE_SIZE, text_poke_area[1] also be PAGE_SIZE, and that the sum of both would be 2 * PAGE_SIZE.. > + BUG_ON(!text_poke_area[0] || !text_poke_area[1]); > +} > + > /** > * text_poke - Update instructions on a live kernel > * @addr: address to modify > @@ -501,8 +511,9 @@ void *__kprobes text_poke(void *addr, co > unsigned long flags; > char *vaddr; > int nr_pages = 2; > - struct page *pages[2]; > - int i; > + struct page *pages[2], **pgp = pages; Hrm, why do you need **pgp ? Could you simply pass &pages to map_vm_area ? Thanks, Mathieu > + int i, ret; > + struct vm_struct *vma; > > if (!core_kernel_text((unsigned long)addr)) { > pages[0] = vmalloc_to_page(addr); > @@ -515,12 +526,16 @@ void *__kprobes text_poke(void *addr, co > BUG_ON(!pages[0]); > if (!pages[1]) > nr_pages = 1; > - vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL); > - BUG_ON(!vaddr); > + spin_lock(&text_poke_lock); > + vma = text_poke_area[nr_pages-1]; > + ret = map_vm_area(vma, PAGE_KERNEL, &pgp); > + BUG_ON(ret); > + vaddr = vma->addr; > local_irq_save(flags); > memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); > local_irq_restore(flags); > - vunmap(vaddr); > + unmap_kernel_range((unsigned long)vma->addr, (unsigned long)vma->size); > + spin_unlock(&text_poke_lock); > sync_core(); > /* Could also do a CLFLUSH here to speed up CPU recovery; but > that causes hangs on some VIA CPUs. */ > @@ -528,3 +543,4 @@ void *__kprobes text_poke(void *addr, co > BUG_ON(((char *)addr)[i] != ((char *)opcode)[i]); > return addr; > } > +EXPORT_SYMBOL_GPL(text_poke); > Index: linux-2.6/init/main.c > =================================================================== > --- linux-2.6.orig/init/main.c > +++ linux-2.6/init/main.c > @@ -676,6 +676,9 @@ asmlinkage void __init start_kernel(void > taskstats_init_early(); > delayacct_init(); > > +#ifdef CONFIG_X86 > + text_poke_init(); > +#endif > check_bugs(); > > acpi_early_init(); /* before LAPIC and SMP init */ -- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68