Messages in this thread Patch in this message | | | Date | Wed, 30 Sep 2009 17:07:54 +0200 | From | Arjan van de Ven <> | Subject | Re: Linux 2.6.32-rc1 |
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On Tue, 29 Sep 2009 14:56:28 -0700 (PDT) Linus Torvalds <torvalds@linux-foundation.org> wrote:
> > > On Tue, 29 Sep 2009, Arjan van de Ven wrote: > > > > can't we use alternatives() for this, to patch cmpxchg64 in ? > > I mean.. it'll be commonly supported nowadays.. the fallback to it > > not being supported could be a bit slower by now... > > Yes, we could. It would limit us to some fixed address format, > probably > > cmpxchg8b (%esi) > > or something. Use something like this as a starting point, perhaps? > > NOTE! Totally untested! And you'd actually need to implement the > "cmpxchg8b_emu" function that takes it's arguments in %eax:%edx, > %ebx:%ecx and %esi and doesn't trash any other registers..
so I debugged this guy (had a few bugs ;-)
patch, including a new cmpxchg8b_emu below:
From 5a76986c5dd272ea16a9b8abb7349ff3d6791c2b Mon Sep 17 00:00:00 2001 From: Arjan van de Ven <arjan@linux.intel.com> Date: Wed, 30 Sep 2009 17:04:35 +0200 Subject: [PATCH] x86: Provide an alternative() based cmpxchg64()
Based on Linus' patch, this patch provides cmpxchg64() using the alternative() infrastructure.
Note: the fallback is NOT smp safe, just like the current fallback is not SMP safe.
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> --- arch/x86/include/asm/cmpxchg_32.h | 29 ++++++++++-------- arch/x86/kernel/i386_ksyms_32.c | 3 ++ arch/x86/lib/Makefile | 2 +- arch/x86/lib/cmpxchg8b_emu.S | 61 +++++++++++++++++++++++++++++++++++++ 4 files changed, 81 insertions(+), 14 deletions(-) create mode 100644 arch/x86/lib/cmpxchg8b_emu.S
diff --git a/arch/x86/include/asm/cmpxchg_32.h b/arch/x86/include/asm/cmpxchg_32.h index 82ceb78..3b21afa 100644 --- a/arch/x86/include/asm/cmpxchg_32.h +++ b/arch/x86/include/asm/cmpxchg_32.h @@ -312,19 +312,22 @@ static inline unsigned long cmpxchg_386(volatile void *ptr, unsigned long old, extern unsigned long long cmpxchg_486_u64(volatile void *, u64, u64); -#define cmpxchg64(ptr, o, n) \ -({ \ - __typeof__(*(ptr)) __ret; \ - if (likely(boot_cpu_data.x86 > 4)) \ - __ret = (__typeof__(*(ptr)))__cmpxchg64((ptr), \ - (unsigned long long)(o), \ - (unsigned long long)(n)); \ - else \ - __ret = (__typeof__(*(ptr)))cmpxchg_486_u64((ptr), \ - (unsigned long long)(o), \ - (unsigned long long)(n)); \ - __ret; \ -}) +#define cmpxchg64(ptr, o, n) \ +({ \ + __typeof__(*(ptr)) __ret; \ + __typeof__(*(ptr)) __old = (o); \ + __typeof__(*(ptr)) __new = (n); \ + alternative_io("call cmpxchg8b_emu", \ + "lock; cmpxchg8b (%%esi)" , \ + X86_FEATURE_CX8, \ + "=A" (__ret), \ + "S" ((ptr)), "0" (__old), \ + "b" ((unsigned int)__new), \ + "c" ((unsigned int)(__new>>32))); \ + __ret; }) + + + #define cmpxchg64_local(ptr, o, n) \ ({ \ __typeof__(*(ptr)) __ret; \ diff --git a/arch/x86/kernel/i386_ksyms_32.c b/arch/x86/kernel/i386_ksyms_32.c index 43cec6b..f17930e 100644 --- a/arch/x86/kernel/i386_ksyms_32.c +++ b/arch/x86/kernel/i386_ksyms_32.c @@ -10,6 +10,9 @@ EXPORT_SYMBOL(mcount); #endif +extern void cmpxchg8b_emu(void); /* dummy proto */ +EXPORT_SYMBOL(cmpxchg8b_emu); + /* Networking helper routines. */ EXPORT_SYMBOL(csum_partial_copy_generic); diff --git a/arch/x86/lib/Makefile b/arch/x86/lib/Makefile index 9e60920..3e549b8 100644 --- a/arch/x86/lib/Makefile +++ b/arch/x86/lib/Makefile @@ -15,7 +15,7 @@ ifeq ($(CONFIG_X86_32),y) obj-y += atomic64_32.o lib-y += checksum_32.o lib-y += strstr_32.o - lib-y += semaphore_32.o string_32.o + lib-y += semaphore_32.o string_32.o cmpxchg8b_emu.o lib-$(CONFIG_X86_USE_3DNOW) += mmx_32.o else diff --git a/arch/x86/lib/cmpxchg8b_emu.S b/arch/x86/lib/cmpxchg8b_emu.S new file mode 100644 index 0000000..b8af4c7 --- /dev/null +++ b/arch/x86/lib/cmpxchg8b_emu.S @@ -0,0 +1,61 @@ +/* + * This program is free software; you can redistribute it and/or + * modify it under the terms of the GNU General Public License + * as published by the Free Software Foundation; version 2 + * of the License. + * + */ + +#include <linux/linkage.h> +#include <asm/alternative-asm.h> +#include <asm/frame.h> +#include <asm/dwarf2.h> + + +.text + +/* + * Inputs: + * %esi : memory location to compare + * %eax : low 32 bits of old value + * %edx : high 32 bits of old value + * %ebx : low 32 bits of new value + * %ecx : high 32 bits of new value + */ +ENTRY(cmpxchg8b_emu) + CFI_STARTPROC + + push %edi + push %ebx + push %ecx + /* disable interrupts */ + pushf + pop %edi + cli + + cmpl %edx, 4(%esi) + jne 1f + cmpl %eax, (%esi) + jne 1f + + xchg (%esi), %ebx + xchg 4(%esi), %ecx + mov %ebx, %eax + mov %ecx, %edx + +2: + /* restore interrupts */ + push %edi + popf + + pop %ecx + pop %ebx + pop %edi + ret +1: + mov (%esi), %eax + mov 4(%esi), %edx + jmp 2b + CFI_ENDPROC +ENDPROC(cmpxchg8b_emu) + -- 1.6.2.5
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