x86: implement atomic text_poke() via fixmap

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>
LKML-Reference: <49B14352.2040705@redhat.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/arch/x86/include/asm/fixmap.h b/arch/x86/include/asm/fixmap.h
index 63a79c7..81937a5 100644 (file)
--- a/arch/x86/include/asm/fixmap.h
+++ b/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,

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 092a7b8..2d903b7 100644 (file)
--- a/arch/x86/kernel/alternative.c
+++ b/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 void *opcode, size_t len)
  * 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, const void *opcode, size_t len)
                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]));
+       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. */