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Message-ID: <20090216172441.GA12576@Krystal>
Date: Mon, 16 Feb 2009 12:24:42 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
To: Nick Piggin <npiggin@...e.de>
Cc: Masami Hiramatsu <mhiramat@...hat.com>,
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
* Nick Piggin (npiggin@...e.de) wrote:
> 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.
>
AFAIK, map_vm_area/unmap_vm_area is faster than vmap/vunmap. This is
the point of this patch. Masami, could you provide a quick benchmark of
text_poke()/seconds before and after this optimization is applied to
confirm this ?
Thanks,
Mathieu
>
> > 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
--
Mathieu Desnoyers
OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
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