linux-kernel - Re: irq-disabled vs vmap vs text

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Message-ID: <20090216153145.GB19182@wotan.suse.de>
Date:	Mon, 16 Feb 2009 16:31:45 +0100
From:	Nick Piggin <npiggin@...e.de>
To:	Masami Hiramatsu <mhiramat@...hat.com>
Cc:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Peter Zijlstra <peterz@...radead.org>,
	akpm <akpm@...ux-foundation.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...e.hu>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>
Subject: Re: irq-disabled vs vmap vs text_poke

On Mon, Feb 16, 2009 at 10:04:43AM -0500, Masami Hiramatsu wrote:
> >>>>>BTW, what about using map_vm_area() in text_poke() instead of vmap()?
> >>>>>Since text_poke() just maps text pages to alias pages temporarily,
> >>>>>I think we don't need to use delayed vunmap().

[...] 

> Here is the patch which replace v(un)map with (un)map_vm_area.

I don't quite understand the point of this... delayed vunmap() is
just an implementation detail of vmap subsystem. Callers should not
have to care.

 
> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.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);
> +	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;
> +	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. */
> 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@...hat.com
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