[PATCH] x86: SMP alternatives

Implement SMP alternatives, i.e.  switching at runtime between different
code versions for UP and SMP.  The code can patch both SMP->UP and UP->SMP.
The UP->SMP case is useful for CPU hotplug.

With CONFIG_CPU_HOTPLUG enabled the code switches to UP at boot time and
when the number of CPUs goes down to 1, and switches to SMP when the number
of CPUs goes up to 2.

Without CONFIG_CPU_HOTPLUG or on non-SMP-capable systems the code is
patched once at boot time (if needed) and the tables are released
afterwards.

The changes in detail:

  * The current alternatives bits are moved to a separate file,
    the SMP alternatives code is added there.

  * The patch adds some new elf sections to the kernel:
    .smp_altinstructions
	like .altinstructions, also contains a list
	of alt_instr structs.
    .smp_altinstr_replacement
	like .altinstr_replacement, but also has some space to
	save original instruction before replaving it.
    .smp_locks
	list of pointers to lock prefixes which can be nop'ed
	out on UP.
    The first two are used to replace more complex instruction
    sequences such as spinlocks and semaphores.  It would be possible
    to deal with the lock prefixes with that as well, but by handling
    them as special case the table sizes become much smaller.

 * The sections are page-aligned and padded up to page size, so they
   can be free if they are not needed.

 * Splitted the code to release init pages to a separate function and
   use it to release the elf sections if they are unused.

Signed-off-by: Gerd Hoffmann <kraxel@suse.de>
Signed-off-by: Chuck Ebbert <76306.1226@compuserve.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

1 files changed, 1 insertions, 61 deletions

diff --git a/include/asm-i386/system.h b/include/asm-i386/system.h
index 399145a247f2..d0d8d7448d88 100644
--- a/include/asm-i386/system.h
+++ b/include/asm-i386/system.h
@@ -352,67 +352,6 @@ static inline unsigned long long __cmpxchg64(volatile void *ptr, unsigned long l
 
 #endif
     
-#ifdef __KERNEL__
-struct alt_instr { 
-        __u8 *instr;            /* original instruction */
-        __u8 *replacement;
-        __u8  cpuid;            /* cpuid bit set for replacement */
-        __u8  instrlen;         /* length of original instruction */
-        __u8  replacementlen;   /* length of new instruction, <= instrlen */ 
-        __u8  pad;
-}; 
-#endif
-
-/* 
- * Alternative instructions for different CPU types or capabilities.
- * 
- * This allows to use optimized instructions even on generic binary
- * kernels.
- * 
- * length of oldinstr must be longer or equal the length of newinstr
- * It can be padded with nops as needed.
- * 
- * For non barrier like inlines please define new variants
- * without volatile and memory clobber.
- */
-#define alternative(oldinstr, newinstr, feature)        \
-        asm volatile ("661:\n\t" oldinstr "\n662:\n"                 \
-                      ".section .altinstructions,\"a\"\n"            \
-                      "  .align 4\n"                                   \
-                      "  .long 661b\n"            /* label */          \
-                      "  .long 663f\n"            /* new instruction */         \
-                      "  .byte %c0\n"             /* feature bit */    \
-                      "  .byte 662b-661b\n"       /* sourcelen */      \
-                      "  .byte 664f-663f\n"       /* replacementlen */ \
-                      ".previous\n"                                             \
-                      ".section .altinstr_replacement,\"ax\"\n"                 \
-                      "663:\n\t" newinstr "\n664:\n"   /* replacement */    \
-                      ".previous" :: "i" (feature) : "memory")  
-
-/*
- * Alternative inline assembly with input.
- * 
- * Pecularities:
- * No memory clobber here. 
- * Argument numbers start with 1.
- * Best is to use constraints that are fixed size (like (%1) ... "r")
- * If you use variable sized constraints like "m" or "g" in the 
- * replacement maake sure to pad to the worst case length.
- */
-#define alternative_input(oldinstr, newinstr, feature, input...)                \
-        asm volatile ("661:\n\t" oldinstr "\n662:\n"                            \
-                      ".section .altinstructions,\"a\"\n"                       \
-                      "  .align 4\n"                                            \
-                      "  .long 661b\n"            /* label */                   \
-                      "  .long 663f\n"            /* new instruction */         \
-                      "  .byte %c0\n"             /* feature bit */             \
-                      "  .byte 662b-661b\n"       /* sourcelen */               \
-                      "  .byte 664f-663f\n"       /* replacementlen */          \
-                      ".previous\n"                                             \
-                      ".section .altinstr_replacement,\"ax\"\n"                 \
-                      "663:\n\t" newinstr "\n664:\n"   /* replacement */        \
-                      ".previous" :: "i" (feature), ##input)
-
 /*
  * Force strict CPU ordering.
  * And yes, this is required on UP too when we're talking
@@ -558,5 +497,6 @@ static inline void sched_cacheflush(void)
 }
 
 extern unsigned long arch_align_stack(unsigned long sp);
+extern void free_init_pages(char *what, unsigned long begin, unsigned long end);
 
 #endif