Messages in this thread | | | Date | Mon, 2 Mar 2009 12:19:14 -0500 | From | Mathieu Desnoyers <> | Subject | Re: [RFC][PATCH] x86: make text_poke() atomic |
| |
* Masami Hiramatsu (mhiramat@redhat.com) wrote: > Masami Hiramatsu wrote: >> Mathieu Desnoyers wrote: >>> * Masami Hiramatsu (mhiramat@redhat.com) wrote: >>>> 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()... >>>> >>> You are right. If we plan to execute this in both atomic and non-atomic >>> context, spin_lock_irqsave would make sure we are always busy-looping >>> with interrupts off. >> >> Oops, when I tested spin_lock_irqsave, it caused warnings. >> >> ------------[ cut here ]------------ >> WARNING: at /home/mhiramat/ksrc/linux-2.6/kernel/smp.c:329 smp_call_function_man >> y+0x37/0x1c9() >> Hardware name: Precision WorkStation T5400 >> Modules linked in: >> Pid: 1, comm: swapper Tainted: G W 2.6.29-rc6 #16 >> Call Trace: >> [<c042f7b1>] warn_slowpath+0x71/0xa8 >> [<c044dccb>] ? trace_hardirqs_on_caller+0x18/0x145 >> [<c06dc42f>] ? _spin_unlock_irq+0x22/0x2f >> [<c044efc9>] ? print_lock_contention_bug+0x14/0xd7 >> [<c044efc9>] ? print_lock_contention_bug+0x14/0xd7 >> [<c044cfbb>] ? trace_hardirqs_off_caller+0x18/0xa3 >> [<c045383b>] smp_call_function_many+0x37/0x1c9 >> [<c04138fc>] ? do_flush_tlb_all+0x0/0x3c >> [<c04138fc>] ? do_flush_tlb_all+0x0/0x3c >> [<c04539e9>] smp_call_function+0x1c/0x23 >> [<c0433ee1>] on_each_cpu+0xf/0x3a >> [<c04138c6>] flush_tlb_all+0x14/0x16 >> [<c04946f7>] unmap_kernel_range+0xf/0x11 >> [<c06dd78a>] text_poke+0xf1/0x12c >> >> unmap_kernel_range() requires irq enabled, but spin_lock_irqsave >> (and stop_machine too)disables irq. so we have to solve this issue. >> >> I have some ideas: >> >> - export(just remove static) vunmap_page_range() and don't use >> flush_tlb_all(). >> Because this vm_area are not used by other cpus, we don't need >> to flush TLB of all cpus. >> >> - make unmap_kernel_range_local() function. >> >> - extend kmap_atomic_prot() to map lowmem page when the 'prot' >> is different. >> > > I updated my patch based on the first idea. > I also checked that text_poke() can be called from stop_machine() > with this patch. > --- > > 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); > @@ -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); > - local_irq_save(flags); > + spin_lock_irqsave(&text_poke_lock, flags); > + vma = text_poke_area[nr_pages-1]; > + ret = map_vm_area(vma, PAGE_KERNEL, &pgp); > + BUG_ON(ret); > + vaddr = vma->addr; > memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len); > - local_irq_restore(flags); > - vunmap(vaddr); > + /* Ported from unmap_kernel_range() */ > + flush_cache_vunmap((unsigned long)vma->addr, (unsigned long)vma->size); > + vunmap_page_range((unsigned long)vma->addr, > + (unsigned long)vma->addr + (unsigned long)vma->size); > + /* > + * Since this mapping is temporary, local and protected by spinlock, > + * we just need to flush TLB on local processor. > + */ > + local_flush_tlb(); > + spin_unlock_irqrestore(&text_poke_lock, flags); > 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
All good, except this above. There should be an empty text_poke_init() in some header file, and an implementation for the X86 arch rather than a ifdef in init/main.c.
Mathieu
> check_bugs(); > > acpi_early_init(); /* before LAPIC and SMP init */ > Index: linux-2.6/mm/vmalloc.c > =================================================================== > --- linux-2.6.orig/mm/vmalloc.c > +++ linux-2.6/mm/vmalloc.c > @@ -71,7 +71,7 @@ static void vunmap_pud_range(pgd_t *pgd, > } while (pud++, addr = next, addr != end); > } > > -static void vunmap_page_range(unsigned long addr, unsigned long end) > +void vunmap_page_range(unsigned long addr, unsigned long end) > { > pgd_t *pgd; > unsigned long next; > Index: linux-2.6/include/linux/vmalloc.h > =================================================================== > --- linux-2.6.orig/include/linux/vmalloc.h > +++ linux-2.6/include/linux/vmalloc.h > @@ -96,6 +96,7 @@ extern struct vm_struct *remove_vm_area( > extern int map_vm_area(struct vm_struct *area, pgprot_t prot, > struct page ***pages); > extern void unmap_kernel_range(unsigned long addr, unsigned long size); > +extern void vunmap_page_range(unsigned long addr, unsigned long end); > > /* Allocate/destroy a 'vmalloc' VM area. */ > extern struct vm_struct *alloc_vm_area(size_t size); > > -- > Masami Hiramatsu > > Software Engineer > Hitachi Computer Products (America) Inc. > Software Solutions Division > > e-mail: mhiramat@redhat.com > >
-- Mathieu Desnoyers OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68
| |