Le samedi 26 mars 2011 Ã 20:57 -0500, Christoph Lameter a Ãcrit :
> But then the same fix must also be used in the asm code or the fallback
> (turns out that the fallback is always used in kmem_cache_init since
> the instruction patching comes later).
>
> Patch boots fine both in UP and SMP mode
>
>
>
>
> Subject: percpu: Omit segment prefix in the UP case for cmpxchg_double
>
> Omit the segment prefix in the UP case. GS is not used then
> and we will generate segfaults if cmpxchg16b is used otherwise.
>
> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Christoph Lameter <cl@xxxxxxxxx>
>
> arch/x86/include/asm/percpu.h | 10 ++++++----
> 1 files changed, 6 insertions(+), 4 deletions(-)
>
> Index: linux-2.6/arch/x86/include/asm/percpu.h
> ===================================================================
> --- linux-2.6.orig/arch/x86/include/asm/percpu.h 2011-03-26 20:43:03.994089001 -0500
> +++ linux-2.6/arch/x86/include/asm/percpu.h 2011-03-26 20:43:22.414089004 -0500
> @@ -45,7 +45,7 @@
> #include <linux/stringify.h>
>
> #ifdef CONFIG_SMP
> -#define __percpu_arg(x) "%%"__stringify(__percpu_seg)":%P" #x
> +#define __percpu_prefix "%%"__stringify(__percpu_seg)":"
> #define __my_cpu_offset percpu_read(this_cpu_off)
>
> /*
> @@ -62,9 +62,11 @@
> (typeof(*(ptr)) __kernel __force *)tcp_ptr__; \
> })
> #else
> -#define __percpu_arg(x) "%P" #x
> +#define __percpu_prefix ""
> #endif
>
> +#define __percpu_arg(x) __percpu_prefix "%P" #x
> +
> /*
> * Initialized pointers to per-cpu variables needed for the boot
> * processor need to use these macros to get the proper address
> @@ -516,11 +518,11 @@
> typeof(o2) __n2 = n2; \
> typeof(o2) __dummy; \
> alternative_io("call this_cpu_cmpxchg16b_emu\n\t" P6_NOP4, \
I guess you should make P6_NOP4 be P6_NOP3 in !SMP builds.
> - "cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t", \
> + "cmpxchg16b " __percpu_prefix "(%%rsi)\n\tsetz %0\n\t", \
> X86_FEATURE_CX16, \
> ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)), \
> "S" (&pcp1), "b"(__n1), "c"(__n2), \
> - "a"(__o1), "d"(__o2)); \
> + "a"(__o1), "d"(__o2) : "memory"); \
> __ret; \
> })
>
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