From: Masami Hiramatsu <mhiramat@redhat.com>
To: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Andi Kleen <andi@firstfloor.org>,
linux-kernel@vger.kernel.org, Ingo Molnar <mingo@elte.hu>,
Andrew Morton <akpm@linux-foundation.org>,
Thomas Gleixner <tglx@linutronix.de>,
Peter Zijlstra <peterz@infradead.org>,
Frederic Weisbecker <fweisbec@gmail.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Arjan van de Ven <arjan@infradead.org>,
Rusty Russell <rusty@rustcorp.com.au>,
"H. Peter Anvin" <hpa@zytor.com>,
Steven Rostedt <srostedt@redhat.com>
Subject: Re: [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions
Date: Fri, 27 Feb 2009 13:34:31 -0500 [thread overview]
Message-ID: <49A83237.40604@redhat.com> (raw)
In-Reply-To: <20090227180724.GA17947@Krystal>
Mathieu Desnoyers wrote:
> * 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 for comments!
I think it could be. ah, spin_lock might be changed to spin_lock_irqsave()...
>> Thank you,
>>
> [...]
>> Use map_vm_area() instead of vmap() in text_poke() for avoiding page allocation
>> and delayed unmapping.
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com>
>> ---
>> 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..
Unfortunately, current map_vm_area() tries to map the size of vm_area,
this means, you can't use 2page-size vm_area for mapping just 1 page...
(or maybe, we can set pages[1] = pages[0] when 2nd page doesn't exist)
>> + 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 ?
As you know, pages means just the address(value) of an array, so you can't
get the address of the address...(pages and &pages are same.)
int array[2];
printf("%p, %p",array, &array);
please try it :)
And actually, map_vm_area() requires the address of a pointer.
---
int map_vm_area(struct vm_struct *area, pgprot_t prot, struct page ***pages)
{
unsigned long addr = (unsigned long)area->addr;
unsigned long end = addr + area->size - PAGE_SIZE;
int err;
err = vmap_page_range(addr, end, prot, *pages);
if (err > 0) {
*pages += err;
^^^^^^^^^^^^^^ Here, it tries to add err(=number of mapped pages)
to the pages pointer!
err = 0;
}
return err;
}
---
>
> 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 */
>
>
--
Masami Hiramatsu
Software Engineer
Hitachi Computer Products (America) Inc.
Software Solutions Division
e-mail: mhiramat@redhat.com
next prev parent reply other threads:[~2009-02-27 18:35 UTC|newest]
Thread overview: 89+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-02-20 1:13 [git pull] changes for tip, and a nasty x86 page table bug Steven Rostedt
2009-02-20 1:13 ` [PATCH 1/6] x86: check PMD in spurious_fault handler Steven Rostedt
2009-02-20 1:13 ` [PATCH 2/6] x86: keep pmd rw bit set when creating 4K level pages Steven Rostedt
2009-02-20 1:13 ` [PATCH 3/6] ftrace: allow archs to preform pre and post process for code modification Steven Rostedt
2009-02-20 1:13 ` [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions Steven Rostedt
2009-02-20 1:32 ` Andrew Morton
2009-02-20 1:44 ` Steven Rostedt
2009-02-20 2:05 ` [PATCH][git pull] update to tip/tracing/ftrace Steven Rostedt
2009-02-22 17:50 ` [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions Andi Kleen
2009-02-22 22:53 ` Steven Rostedt
2009-02-23 0:29 ` Andi Kleen
2009-02-23 2:33 ` Mathieu Desnoyers
2009-02-23 4:29 ` Steven Rostedt
2009-02-23 4:53 ` Mathieu Desnoyers
2009-02-23 14:48 ` Steven Rostedt
2009-02-23 15:42 ` Mathieu Desnoyers
2009-02-23 15:51 ` Steven Rostedt
2009-02-23 15:55 ` Steven Rostedt
2009-02-23 16:13 ` Mathieu Desnoyers
2009-02-23 16:48 ` Steven Rostedt
2009-02-23 17:31 ` Mathieu Desnoyers
2009-02-23 18:17 ` Steven Rostedt
2009-02-23 18:34 ` Mathieu Desnoyers
2009-02-27 17:52 ` Masami Hiramatsu
2009-02-27 18:07 ` Mathieu Desnoyers
2009-02-27 18:34 ` Masami Hiramatsu [this message]
2009-02-27 18:53 ` Mathieu Desnoyers
2009-02-27 20:57 ` Masami Hiramatsu
2009-03-02 17:01 ` [RFC][PATCH] x86: make text_poke() atomic Masami Hiramatsu
2009-03-02 17:19 ` Mathieu Desnoyers
2009-03-02 22:15 ` Masami Hiramatsu
2009-03-02 22:22 ` Ingo Molnar
2009-03-02 22:55 ` Masami Hiramatsu
2009-03-02 23:09 ` Ingo Molnar
2009-03-02 23:38 ` Masami Hiramatsu
2009-03-02 23:49 ` Ingo Molnar
2009-03-03 0:00 ` Mathieu Desnoyers
2009-03-03 0:00 ` [PATCH] Text Edit Lock - Architecture Independent Code Mathieu Desnoyers
2009-03-03 0:32 ` Ingo Molnar
2009-03-03 0:39 ` Mathieu Desnoyers
2009-03-03 1:30 ` [PATCH] Text Edit Lock - Architecture Independent Code (v2) Mathieu Desnoyers
2009-03-03 1:31 ` [PATCH] Text Edit Lock - kprobes architecture independent support (v2) Mathieu Desnoyers
2009-03-03 9:27 ` Ingo Molnar
2009-03-03 12:06 ` Ananth N Mavinakayanahalli
2009-03-03 14:28 ` Mathieu Desnoyers
2009-03-03 14:33 ` [PATCH] Text Edit Lock - kprobes architecture independent support (v3) Mathieu Desnoyers
2009-03-03 14:53 ` [PATCH] Text Edit Lock - kprobes architecture independent support (v2) Ingo Molnar
2009-03-03 0:01 ` [PATCH] Text Edit Lock - kprobes architecture independent support Mathieu Desnoyers
2009-03-03 0:10 ` Masami Hiramatsu
2009-03-03 0:05 ` [RFC][PATCH] x86: make text_poke() atomic Masami Hiramatsu
2009-03-03 0:22 ` Ingo Molnar
2009-03-03 0:31 ` Masami Hiramatsu
2009-03-03 16:31 ` [PATCH] x86: make text_poke() atomic using fixmap Masami Hiramatsu
2009-03-03 17:08 ` Mathieu Desnoyers
2009-03-05 10:38 ` Ingo Molnar
2009-03-06 14:06 ` Ingo Molnar
2009-03-06 14:49 ` Masami Hiramatsu
2009-03-02 18:28 ` [RFC][PATCH] x86: make text_poke() atomic Arjan van de Ven
2009-03-02 18:36 ` Mathieu Desnoyers
2009-03-02 18:55 ` Arjan van de Ven
2009-03-02 19:13 ` Masami Hiramatsu
2009-03-02 19:23 ` H. Peter Anvin
2009-03-02 19:47 ` Mathieu Desnoyers
2009-03-02 18:42 ` Linus Torvalds
2009-03-03 4:54 ` Nick Piggin
2009-02-23 18:23 ` [PATCH 4/6] ftrace, x86: make kernel text writable only for conversions Steven Rostedt
2009-02-23 9:02 ` Ingo Molnar
2009-02-27 21:08 ` Pavel Machek
2009-02-28 16:56 ` Andi Kleen
2009-02-28 22:08 ` Pavel Machek
[not found] ` <87wsba1a9f.fsf@basil.nowhere.org>
2009-02-28 22:19 ` Pavel Machek
2009-02-28 23:52 ` Andi Kleen
2009-02-20 1:13 ` [PATCH 5/6] ftrace: immediately stop code modification if failure is detected Steven Rostedt
2009-02-20 1:13 ` [PATCH 6/6] ftrace: break out modify loop immediately on detection of error Steven Rostedt
2009-02-20 2:00 ` [git pull] changes for tip, and a nasty x86 page table bug Linus Torvalds
2009-02-20 2:08 ` Steven Rostedt
2009-02-20 3:44 ` Linus Torvalds
2009-02-20 4:00 ` Steven Rostedt
2009-02-20 4:17 ` Linus Torvalds
2009-02-20 4:34 ` Steven Rostedt
2009-02-20 5:02 ` Huang Ying
2009-02-20 7:29 ` [PATCH] x86: use the right protections for split-up pagetables Ingo Molnar
2009-02-20 7:39 ` [PATCH, v2] " Ingo Molnar
2009-02-20 8:02 ` Ingo Molnar
2009-02-20 10:24 ` Ingo Molnar
2009-02-20 13:57 ` [PATCH] " Steven Rostedt
2009-02-20 15:40 ` Linus Torvalds
2009-02-20 16:59 ` Ingo Molnar
2009-02-20 18:33 ` H. Peter Anvin
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