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    SubjectRe: [RFC][PATCH] x86: make text_poke() atomic
    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@redhat.com>
    > Cc: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
    > Cc: Nick Piggin <npiggin@suse.de>
    > ---
    > 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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