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SubjectRe: [PATCH -tip 4/4] Atomic text_poke() with fixmap
* Masami Hiramatsu (mhiramat@redhat.com) wrote:
> Use fixmaps instead of vmap/vunmap in text_poke() for avoiding page allocation
> and delayed unmapping.
>
> 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>
> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
> Cc: Ingo Molnar <mingo@elte.hu>
> ---
> arch/x86/include/asm/fixmap.h | 2 ++
> arch/x86/kernel/alternative.c | 24 +++++++++++++++---------
> 2 files changed, 17 insertions(+), 9 deletions(-)
>
> Index: linux-2.6-tip/arch/x86/kernel/alternative.c
> ===================================================================
> --- linux-2.6-tip.orig/arch/x86/kernel/alternative.c
> +++ linux-2.6-tip/arch/x86/kernel/alternative.c
> @@ -13,7 +13,9 @@
> #include <asm/nmi.h>
> #include <asm/vsyscall.h>
> #include <asm/cacheflush.h>
> +#include <asm/tlbflush.h>
> #include <asm/io.h>
> +#include <asm/fixmap.h>
>
> #define MAX_PATCH_LEN (255-1)
>
> @@ -505,15 +507,16 @@ void *text_poke_early(void *addr, const
> * It means the size must be writable atomically and the address must be aligned
> * in a way that permits an atomic write. It also makes sure we fit on a single
> * page.
> + *
> + * Note: Must be called under text_mutex.
> */
> void *__kprobes text_poke(void *addr, const void *opcode, size_t len)
> {
> + unsigned long flags;
> char *vaddr;
> - int nr_pages = 2;
> struct page *pages[2];
> int i;
>
> - might_sleep();
> if (!core_kernel_text((unsigned long)addr)) {
> pages[0] = vmalloc_to_page(addr);
> pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
> @@ -523,14 +526,17 @@ void *__kprobes text_poke(void *addr, co
> pages[1] = virt_to_page(addr + PAGE_SIZE);
> }
> BUG_ON(!pages[0]);
> - if (!pages[1])
> - nr_pages = 1;
> - vaddr = vmap(pages, nr_pages, VM_MAP, PAGE_KERNEL);
> - BUG_ON(!vaddr);
> - local_irq_disable();
> + set_fixmap(FIX_TEXT_POKE0, page_to_phys(pages[0]));

Can the set_fixmap/clear_fixmap/local_flush_tlb be called within
local_irq_save ? If yes, that would be better, especially for the SMP
alternatives code, which would rely on interrupt disabling in text_poke
for consistency (the mutex is not needed there).

Mathieu

> + if (pages[1])
> + set_fixmap(FIX_TEXT_POKE1, page_to_phys(pages[1]));
> + vaddr = (char *)fix_to_virt(FIX_TEXT_POKE0);
> + local_irq_save(flags);
> memcpy(&vaddr[(unsigned long)addr & ~PAGE_MASK], opcode, len);
> - local_irq_enable();
> - vunmap(vaddr);
> + local_irq_restore(flags);
> + clear_fixmap(FIX_TEXT_POKE0);
> + if (pages[1])
> + clear_fixmap(FIX_TEXT_POKE1);
> + local_flush_tlb();
> 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-tip/arch/x86/include/asm/fixmap.h
> ===================================================================
> --- linux-2.6-tip.orig/arch/x86/include/asm/fixmap.h
> +++ linux-2.6-tip/arch/x86/include/asm/fixmap.h
> @@ -111,6 +111,8 @@ enum fixed_addresses {
> #ifdef CONFIG_PARAVIRT
> FIX_PARAVIRT_BOOTMAP,
> #endif
> + FIX_TEXT_POKE0, /* reserve 2 pages for text_poke() */
> + FIX_TEXT_POKE1,
> __end_of_permanent_fixed_addresses,
> #ifdef CONFIG_PROVIDE_OHCI1394_DMA_INIT
> FIX_OHCI1394_BASE,
> --
> 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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