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Subject[thisops uV2 09/10] x86: this_cpu_cmpxchg and this_cpu_cmpxchg_double operations
Provide support as far as the hardware capabilities of the x86 cpus
allow.

V1->V2:
- Mark %rdx clobbering during cmpxchg16b
- Provide emulation of cmpxchg16b for early AMD processors

Signed-off-by: Christoph Lameter <cl@linux.com>

---
arch/x86/include/asm/percpu.h | 122 +++++++++++++++++++++++++++++++++++++++++-
arch/x86/lib/Makefile | 1
arch/x86/lib/cmpxchg16b_emu.S | 55 ++++++++++++++++++
3 files changed, 177 insertions(+), 1 deletion(-)
Index: linux-2.6/arch/x86/include/asm/percpu.h
===================================================================
--- linux-2.6.orig/arch/x86/include/asm/percpu.h 2010-11-26 12:37:37.000000000 -0600
+++ linux-2.6/arch/x86/include/asm/percpu.h 2010-11-26 14:42:49.000000000 -0600
@@ -216,6 +216,41 @@ do { \
pfo_ret__ + (val); \
})

+#define percpu_cmpxchg_op(var, oval, nval) \
+({ \
+ typeof(var) __ret; \
+ typeof(var) __old = (oval); \
+ typeof(var) __new = (nval); \
+ switch (sizeof(var)) { \
+ case 1: \
+ asm("cmpxchgb %2, "__percpu_arg(1) \
+ : "=a" (__ret), "+m" (&var) \
+ : "q" (__new), "0" (__old) \
+ : "memory"); \
+ break; \
+ case 2: \
+ asm("cmpxchgw %2, "__percpu_arg(1) \
+ : "=a" (__ret), "+m" (&var) \
+ : "r" (__new), "0" (__old) \
+ : "memory"); \
+ break; \
+ case 4: \
+ asm("cmpxchgl %2, "__percpu_arg(1) \
+ : "=a" (__ret), "+m" (&var) \
+ : "r" (__new), "0" (__old) \
+ : "memory"); \
+ break; \
+ case 8: \
+ asm("cmpxchgq %2, "__percpu_arg(1) \
+ : "=a" (__ret), "+m" (&var) \
+ : "r" (__new), "0" (__old) \
+ : "memory"); \
+ break; \
+ default: __bad_percpu_size(); \
+ } \
+ __ret; \
+})
+
#define percpu_from_op(op, var, constraint) \
({ \
typeof(var) pfo_ret__; \
@@ -346,7 +381,56 @@ do { \
#define this_cpu_add_return_1(pcp, val) percpu_add_return_op((pcp), val)
#define this_cpu_add_return_2(pcp, val) percpu_add_return_op((pcp), val)
#define this_cpu_add_return_4(pcp, val) percpu_add_return_op((pcp), val)
-#endif
+
+#define __this_cpu_cmpxchg_1(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define __this_cpu_cmpxchg_2(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define __this_cpu_cmpxchg_4(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define this_cpu_cmpxchg_1(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define this_cpu_cmpxchg_2(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define this_cpu_cmpxchg_4(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#endif /* !CONFIG_M386 */
+
+#ifdef CONFIG_X86_CMPXCHG64
+#define percpu_cmpxchg8b_double(pcp, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ typeof(o1) __o1 = o1; \
+ typeof(o1) __n1 = n1; \
+ typeof(o2) __o2 = o2; \
+ typeof(o2) __n2 = n2; \
+ typeof(o2) __dummy = n2; \
+ asm("cmpxchg8b "__percpu_arg(1)"\n\tsetz %0\n\t" \
+ : "=a"(__ret), "=m" (*pcp), "=d"(__dummy) \
+ : "b"(__n1), "c"(__n2), "a"(__o1), "d"(__o2)); \
+ __ret; \
+})
+#endif /* CONFIG_X86_CMPXCHG64 */
+
+#define __this_cpu_cmpxchg_double_4(pcp, o1, o2, n1, n2) percpu_cmpxchg8b_double((pcp), o1, o2, n1, n2)
+#define this_cpu_cmpxchg_double_4(pcp, o1, o2, n1, n2) percpu_cmpxchg8b_double((pcp), o1, o2, n1, n2)
+#define irqsafe_cmpxchg_double_4(pcp, o1, o2, n1, n2) percpu_cmpxchg8b_double((pcp), o1, o2, n1, n2)
+
+#ifndef CONFIG_X86_64
+#ifdef CONFIG_X86_CMPXCHG64
+/* We can support a 8 byte cmpxchg with a special instruction on 32 bit */
+#define __this_cpu_cmpxchg_8(pcp, oval, nval) \
+({ \
+ typeof(var) __ret; \
+ typeof(var) __old = (oval); \
+ typeof(var) __new = (nval); \
+ asm("cmpxchg8b %2, "__percpu_arg(1) \
+ : "=A" (__ret), "+m" (&pcp) \
+ : "b" (((u32)new), "c" ((u32)(new >> 32)), "0" (__old) \
+ : "memory"); \
+ __ret; \
+})
+
+#define this_cpu_cmpxchg_8(pcp, oval, nval) __this_cpu_cmpxchg_8(pcp, oval, nval)
+#define irqsafe_cmpxchg_8(pcp, oval, nval) __this_cpu_cmpxchg_8(pcp, oval, nval)
+
+#endif /* CONFIG_X86_CMPXCHG64 */
+#endif /* !CONFIG_X86_64 */
+
/*
* Per cpu atomic 64 bit operations are only available under 64 bit.
* 32 bit must fall back to generic operations.
@@ -374,6 +458,42 @@ do { \
#define __this_cpu_add_return_8(pcp, val) percpu_add_return_op((pcp), val)
#define this_cpu_add_return_8(pcp, val) percpu_add_return_op((pcp), val)

+#define __this_cpu_cmpxchg_8(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+#define this_cpu_cmpxchg_8(pcp, oval, nval) percpu_cmpxchg_op((pcp), oval, nval)
+
+/*
+ * Pretty complex macro to generate cmpxchg16 instruction. The instruction
+ * is not supported on early AMD64 processors so we must be able to emulate
+ * it in software. The address used in the cmpxchg16 instruction must be
+ * aligned to a 16 byte boundary.
+ */
+
+/*
+ * Something is screwed up with alternate instruction creation. This one
+ * fails with a mysterious asm error about a byte val > 255.
+ */
+#define percpu_cmpxchg16b(pcp, o1, o2, n1, n2) \
+({ \
+ char __ret; \
+ typeof(o1) __o1 = o1; \
+ typeof(o1) __n1 = n1; \
+ typeof(o2) __o2 = o2; \
+ typeof(o2) __n2 = n2; \
+ typeof(o2) __dummy; \
+ VM_BUG_ON(((unsigned long)pcp) % 16); \
+ alternative_io("call cmpxchg16b_local\n\t" P6_NOP4, \
+ "cmpxchg16b %%gs:(%%rsi)\n\tsetz %0\n\t", \
+ X86_FEATURE_CX16, \
+ ASM_OUTPUT2("=a"(__ret), "=d"(__dummy)), \
+ "S" (pcp), "b"(__n1), "c"(__n2), \
+ "a"(__o1), "d"(__o2)); \
+ __ret; \
+})
+
+#define __this_cpu_cmpxchg_double_8(pcp, o1, o2, n1, n2) percpu_cmpxchg16b((pcp), o1, o2, n1, n2)
+#define this_cpu_cmpxchg_double_8(pcp, o1, o2, n1, n2) percpu_cmpxchg16b((pcp), o1, o2, n1, n2)
+#define irqsafe_cmpxchg_double_8(pcp, o1, o2, n1, n2) percpu_cmpxchg16b((pcp), o1, o2, n1, n2)
+
#endif

/* This is not atomic against other CPUs -- CPU preemption needs to be off */
Index: linux-2.6/arch/x86/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/x86/lib/Makefile 2010-11-26 12:08:33.000000000 -0600
+++ linux-2.6/arch/x86/lib/Makefile 2010-11-26 12:50:50.000000000 -0600
@@ -42,4 +42,5 @@ else
lib-y += memmove_64.o memset_64.o
lib-y += copy_user_64.o rwlock_64.o copy_user_nocache_64.o
lib-$(CONFIG_RWSEM_XCHGADD_ALGORITHM) += rwsem_64.o
+ lib-y += cmpxchg16b_emu.o
endif
Index: linux-2.6/arch/x86/lib/cmpxchg16b_emu.S
===================================================================
--- /dev/null 1970-01-01 00:00:00.000000000 +0000
+++ linux-2.6/arch/x86/lib/cmpxchg16b_emu.S 2010-11-26 13:14:02.000000000 -0600
@@ -0,0 +1,55 @@
+/*
+ * 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:
+ * %rsi : memory location to compare
+ * %rax : low 64 bits of old value
+ * %rdx : high 64 bits of old value
+ * %rbx : low 64 bits of new value
+ * %rcx : high 64 bits of new value
+ * %al : Operation successful
+ */
+ENTRY(cmpxchg16b_local_emu)
+CFI_STARTPROC
+
+#
+# Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in
+# al not via the ZF. Caller will access al to get result.
+#
+cmpxchg16b_local_emu:
+ pushf
+ cli
+
+ cmpq %gs:(%rsi), %rax
+ jne not_same
+ cmpq %gs:8(%rsi), %rdx
+ jne not_same
+
+ movq %rbx, %gs:(%esi)
+ movq %rcx, %gs:8(%esi)
+
+ popf
+ mov $1, %al
+ ret
+
+ not_same:
+ popf
+ xor %al,%al
+ ret
+
+CFI_ENDPROC
+ENDPROC(cmpxchg16b_local_emu)


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