Re: [RFC][PATCH] x86: make text_poke() atomic

[Nick Piggin]

On Mon, Mar 02, 2009 at 12:01:29PM -0500, Masami Hiramatsu wrote:
> ---
> 
> Use map_vm_area() instead of vmap() in text_poke() for avoiding page 
> allocation
> and delayed unmapping, and call vunmap_page_range() and local_flush_tlb()
> directly because this mapping is temporary and local.
> 
> At the result of above change, text_poke() becomes atomic and can be called
> from stop_machine() etc.
> 
> Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
> Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>
> Cc: Nick Piggin <npiggin@xxxxxxx>
> ---
>  arch/x86/include/asm/alternative.h |    1 +
>  arch/x86/kernel/alternative.c      |   36 
>  +++++++++++++++++++++++++++++-------
>  include/linux/vmalloc.h            |    1 +
>  init/main.c                        |    3 +++
>  mm/vmalloc.c                       |    2 +-
>  5 files changed, 35 insertions(+), 8 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
> @@ -12,6 +12,7 @@
>  #include <asm/nmi.h>
>  #include <asm/vsyscall.h>
>  #include <asm/cacheflush.h>
> +#include <asm/tlbflush.h>
>  #include <asm/io.h>
> 
>  #define MAX_PATCH_LEN (255-1)
> @@ -485,6 +486,16 @@ 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 +512,9 @@ 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);

This is really good....

> @@ -515,12 +527,22 @@ 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);
        ^^^^^^^^^^^^^^
This really is nasty bug in text_poke, and I never knew why it was
allowed to live for so long!

Thanks,
Nick
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