Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752741AbbKLB2l (ORCPT ); Wed, 11 Nov 2015 20:28:41 -0500 Received: from ozlabs.org ([103.22.144.67]:48592 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752394AbbKLB2k (ORCPT ); Wed, 11 Nov 2015 20:28:40 -0500 From: Rusty Russell To: Josh Poimboeuf Cc: linux-kernel@vger.kernel.org, Peter Zijlstra Subject: Re: [PATCH 4/4] module: clean up RO/NX handling. In-Reply-To: <20151110042736.GA18117@treble.hsd1.ky.comcast.net> References: <1447043037-10833-1-git-send-email-rusty@rustcorp.com.au> <1447043037-10833-5-git-send-email-rusty@rustcorp.com.au> <20151109195153.GB3914@treble.redhat.com> <87611ak44x.fsf@rustcorp.com.au> <20151110042736.GA18117@treble.hsd1.ky.comcast.net> User-Agent: Notmuch/0.20.2 (http://notmuchmail.org) Emacs/24.5.1 (x86_64-pc-linux-gnu) Date: Thu, 12 Nov 2015 11:58:25 +1030 Message-ID: <87bnb0vwee.fsf@rustcorp.com.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6126 Lines: 151 Josh Poimboeuf writes: > On Tue, Nov 10, 2015 at 12:27:34PM +1030, Rusty Russell wrote: >> Josh Poimboeuf writes: >> > On Mon, Nov 09, 2015 at 02:53:57PM +1030, Rusty Russell wrote: >> > >> >> @@ -1858,74 +1849,75 @@ static void mod_sysfs_teardown(struct module *mod) >> >> /* >> >> * LKM RO/NX protection: protect module's text/ro-data >> >> * from modification and any data from execution. >> >> + * >> >> + * General layout of module is: >> >> + * [text] [read-only-data] [writable data] >> >> + * text_size -----^ ^ ^ >> >> + * ro_size ------------------------| | >> >> + * size -------------------------------------------| >> >> + * >> >> + * These values are always page-aligned (as is base) >> >> */ >> >> -void set_page_attributes(void *start, void *end, int (*set)(unsigned long start, int num_pages)) >> >> +static void frob_text(const struct module_layout *layout, >> >> + int (*set_memory)(unsigned long start, int num_pages)) >> >> { >> >> - unsigned long begin_pfn = PFN_DOWN((unsigned long)start); >> >> - unsigned long end_pfn = PFN_DOWN((unsigned long)end); >> >> - >> >> - if (end_pfn > begin_pfn) >> >> - set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn); >> >> + BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1)); >> >> + BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1)); >> >> + set_memory((unsigned long)layout->base, >> >> + layout->text_size >> PAGE_SHIFT); >> > >> > Should the set_memory() call be skipped if text_size is 0? >> >> Not AFAICT. And in practice: >> 1) Every module on my system has a .text section. >> 2) Every module has a rodata section (.modinfo) >> 3) Every module on my system has a .data section. >> >> So I think it would be a premature optimization. > > However, the frob functions are also used for init sections. > > A search on my Fedora system's modules for .init.* sections shows that > most modules don't have .init.rodata and .init.data, and some modules > don't even have .init.text. Good point! OK, let's do some trivial benchmarking... diff --git a/kernel/module.c b/kernel/module.c index 77212128f34a..94ea51a20958 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -1906,10 +1906,19 @@ void module_enable_ro(const struct module *mod) static void module_enable_nx(const struct module *mod) { + size_t i; + ktime_t start, end; frob_rodata(&mod->core_layout, set_memory_nx); frob_writable_data(&mod->core_layout, set_memory_nx); - frob_rodata(&mod->init_layout, set_memory_nx); - frob_writable_data(&mod->init_layout, set_memory_nx); + + start = ktime_get_boottime(); + for (i = 0; i < 1000000; i++) { + frob_rodata(&mod->init_layout, set_memory_nx); + frob_writable_data(&mod->init_layout, set_memory_nx); + } + end = ktime_get_boottime(); + printk("%s init time (ns): %lu\n", module_name(mod), + ktime_to_ns(ktime_sub(end, start))); } static void module_disable_nx(const struct module *mod) [ 2.794462] parport init time (ns): 15277714 [ 2.855277] lp init time (ns): 15207768 [ 2.909701] mac_hid init time (ns): 15409571 [ 2.975350] tpm_tis init time (ns): 15118394 [ 3.062865] parport_pc init time (ns): 15646948 [ 3.247979] virtio_balloon init time (ns): 15555578 [ 3.291373] virtio_net init time (ns): 15236362 [ 3.391361] serio_raw init time (ns): 15395063 Range & mean: 15118394-15646948(1.53559e+07+/-1.7e+05) With a zero-check: [ 2.530933] parport init time (ns): 12133350 [ 2.587167] lp init time (ns): 12059255 [ 2.642342] mac_hid init time (ns): 12849836 [ 2.698726] tpm_tis init time (ns): 12008736 [ 2.768969] parport_pc init time (ns): 12057191 [ 2.943308] virtio_net init time (ns): 12048224 [ 2.989983] virtio_balloon init time (ns): 12077151 [ 3.061752] serio_raw init time (ns): 12396804 Range & mean: 12008736-12849836(1.22038e+07+/-2.7e+05) So, we did save 3ns, but it was 12ns even to call them to do nothing. We'd save more by removing the BUG_ON checks I suspect... Cheers, Rusty. diff --git a/kernel/module.c b/kernel/module.c index 77212128f34a..9ac8952a0a72 100644 --- a/kernel/module.c +++ b/kernel/module.c @@ -1863,8 +1863,9 @@ static void frob_text(const struct module_layout *layout, { BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1)); BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1)); - set_memory((unsigned long)layout->base, - layout->text_size >> PAGE_SHIFT); + if (layout->text_size) + set_memory((unsigned long)layout->base, + layout->text_size >> PAGE_SHIFT); } static void frob_rodata(const struct module_layout *layout, @@ -1873,8 +1874,9 @@ static void frob_rodata(const struct module_layout *layout, BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1)); BUG_ON((unsigned long)layout->text_size & (PAGE_SIZE-1)); BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1)); - set_memory((unsigned long)layout->base + layout->text_size, - (layout->ro_size - layout->text_size) >> PAGE_SHIFT); + if (layout->ro_size != layout->text_size) + set_memory((unsigned long)layout->base + layout->text_size, + (layout->ro_size - layout->text_size) >> PAGE_SHIFT); } static void frob_writable_data(const struct module_layout *layout, @@ -1883,8 +1885,9 @@ static void frob_writable_data(const struct module_layout *layout, BUG_ON((unsigned long)layout->base & (PAGE_SIZE-1)); BUG_ON((unsigned long)layout->ro_size & (PAGE_SIZE-1)); BUG_ON((unsigned long)layout->size & (PAGE_SIZE-1)); - set_memory((unsigned long)layout->base + layout->ro_size, - (layout->size - layout->ro_size) >> PAGE_SHIFT); + if (layout->size != layout->ro_size) + set_memory((unsigned long)layout->base + layout->ro_size, + (layout->size - layout->ro_size) >> PAGE_SHIFT); } /* livepatching wants to disable read-only so it can frob module. */ -- 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/