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>

1 files changed, 15 insertions, 9 deletions

diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c
index 092a7b8be68d..2d903b760ddb 100644
--- 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. */