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    SubjectRe: [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


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