[PATCH 06/12] percpu: Wire up cmpxchg128

Peter Zijlstra
2023-05-31T13:28:46Z

In order to replace cmpxchg_double() with the newly minted
cmpxchg128() family of functions, wire it up in this_cpu_cmpxchg().

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
---
arch/arm64/include/asm/percpu.h | 20 ++++++++++
arch/s390/include/asm/percpu.h | 16 ++++++++
arch/x86/include/asm/percpu.h | 74 ++++++++++++++++++++++++++++++++++++----
arch/x86/lib/Makefile | 3 +
arch/x86/lib/cmpxchg16b_emu.S | 43 +++++++++++++----------
arch/x86/lib/cmpxchg8b_emu.S | 67 ++++++++++++++++++++++++++++--------
include/asm-generic/percpu.h | 56 ++++++++++++++++++++++++++++++
7 files changed, 240 insertions(+), 39 deletions(-)

--- a/arch/arm64/include/asm/percpu.h
+++ b/arch/arm64/include/asm/percpu.h
@@ -140,6 +140,10 @@ PERCPU_RET_OP(add, add, ldadd)
* re-enabling preemption for preemptible kernels, but doing that in a way
* which builds inside a module would mean messing directly with the preempt
* count. If you do this, peterz and tglx will hunt you down.
+ *
+ * Not to mention it'll break the actual preemption model for missing a
+ * preemption point when TIF_NEED_RESCHED gets set while preemption is
+ * disabled.
*/
#define this_cpu_cmpxchg_double_8(ptr1, ptr2, o1, o2, n1, n2) \
({ \
@@ -240,6 +244,22 @@ PERCPU_RET_OP(add, add, ldadd)
#define this_cpu_cmpxchg_8(pcp, o, n) \
_pcp_protect_return(cmpxchg_relaxed, pcp, o, n)

+#define this_cpu_cmpxchg64(pcp, o, n) this_cpu_cmpxchg_8(pcp, o, n)
+
+#define this_cpu_cmpxchg128(pcp, o, n) \
+({ \
+ typedef typeof(pcp) pcp_op_T__; \
+ u128 old__, new__, ret__; \
+ pcp_op_T__ *ptr__; \
+ old__ = o; \
+ new__ = n; \
+ preempt_disable_notrace(); \
+ ptr__ = raw_cpu_ptr(&(pcp)); \
+ ret__ = cmpxchg128_local((void *)ptr__, old__, new__); \
+ preempt_enable_notrace(); \
+ ret__; \
+})
+
#ifdef __KVM_NVHE_HYPERVISOR__
extern unsigned long __hyp_per_cpu_offset(unsigned int cpu);
#define __per_cpu_offset
--- a/arch/s390/include/asm/percpu.h
+++ b/arch/s390/include/asm/percpu.h
@@ -148,6 +148,22 @@
#define this_cpu_cmpxchg_4(pcp, oval, nval) arch_this_cpu_cmpxchg(pcp, oval, nval)
#define this_cpu_cmpxchg_8(pcp, oval, nval) arch_this_cpu_cmpxchg(pcp, oval, nval)

+#define this_cpu_cmpxchg64(pcp, o, n) this_cpu_cmpxchg_8(pcp, o, n)
+
+#define this_cpu_cmpxchg128(pcp, oval, nval) \
+({ \
+ typedef typeof(pcp) pcp_op_T__; \
+ u128 old__, new__, ret__; \
+ pcp_op_T__ *ptr__; \
+ old__ = oval; \
+ new__ = nval; \
+ preempt_disable_notrace(); \
+ ptr__ = raw_cpu_ptr(&(pcp)); \
+ ret__ = cmpxchg128((void *)ptr__, old__, new__); \
+ preempt_enable_notrace(); \
+ ret__; \
+})
+
#define arch_this_cpu_xchg(pcp, nval) \
({ \
typeof(pcp) *ptr__; \
--- a/arch/x86/include/asm/percpu.h
+++ b/arch/x86/include/asm/percpu.h
@@ -210,6 +210,67 @@ do { \
(typeof(_var))(unsigned long) pco_old__; \
})

+#if defined(CONFIG_X86_32) && !defined(CONFIG_UML)
+#define percpu_cmpxchg64_op(size, qual, _var, _oval, _nval) \
+({ \
+ union { \
+ u64 var; \
+ struct { \
+ u32 low, high; \
+ }; \
+ } old__, new__; \
+ \
+ old__.var = _oval; \
+ new__.var = _nval; \
+ \
+ asm qual (ALTERNATIVE("leal %P[var], %%esi; call this_cpu_cmpxchg8b_emu", \
+ "cmpxchg8b " __percpu_arg([var]), X86_FEATURE_CX8) \
+ : [var] "+m" (_var), \
+ "+a" (old__.low), \
+ "+d" (old__.high) \
+ : "b" (new__.low), \
+ "c" (new__.high) \
+ : "memory", "esi"); \
+ \
+ old__.var; \
+})
+
+#define raw_cpu_cmpxchg64(pcp, oval, nval) percpu_cmpxchg64_op(8, , pcp, oval, nval)
+#define this_cpu_cmpxchg64(pcp, oval, nval) percpu_cmpxchg64_op(8, volatile, pcp, oval, nval)
+#endif
+
+#ifdef CONFIG_X86_64
+#define raw_cpu_cmpxchg64(pcp, oval, nval) percpu_cmpxchg_op(8, , pcp, oval, nval);
+#define this_cpu_cmpxchg64(pcp, oval, nval) percpu_cmpxchg_op(8, volatile, pcp, oval, nval);
+
+#define percpu_cmpxchg128_op(size, qual, _var, _oval, _nval) \
+({ \
+ union { \
+ u128 var; \
+ struct { \
+ u64 low, high; \
+ }; \
+ } old__, new__; \
+ \
+ old__.var = _oval; \
+ new__.var = _nval; \
+ \
+ asm qual (ALTERNATIVE("leaq %P[var], %%rsi; call this_cpu_cmpxchg16b_emu", \
+ "cmpxchg16b " __percpu_arg([var]), X86_FEATURE_CX16) \
+ : [var] "+m" (_var), \
+ "+a" (old__.low), \
+ "+d" (old__.high) \
+ : "b" (new__.low), \
+ "c" (new__.high) \
+ : "memory", "rsi"); \
+ \
+ old__.var; \
+})
+
+#define raw_cpu_cmpxchg128(pcp, oval, nval) percpu_cmpxchg128_op(16, , pcp, oval, nval)
+#define this_cpu_cmpxchg128(pcp, oval, nval) percpu_cmpxchg128_op(16, volatile, pcp, oval, nval)
+#endif
+
/*
* this_cpu_read() makes gcc load the percpu variable every time it is
* accessed while this_cpu_read_stable() allows the value to be cached.
@@ -341,12 +402,13 @@ do { \
bool __ret; \
typeof(pcp1) __o1 = (o1), __n1 = (n1); \
typeof(pcp2) __o2 = (o2), __n2 = (n2); \
- alternative_io("leaq %P1,%%rsi\n\tcall this_cpu_cmpxchg16b_emu\n\t", \
- "cmpxchg16b " __percpu_arg(1) "\n\tsetz %0\n\t", \
- X86_FEATURE_CX16, \
- ASM_OUTPUT2("=a" (__ret), "+m" (pcp1), \
- "+m" (pcp2), "+d" (__o2)), \
- "b" (__n1), "c" (__n2), "a" (__o1) : "rsi"); \
+ asm volatile (ALTERNATIVE("leaq %P1, %%rsi; call this_cpu_cmpxchg16b_emu", \
+ "cmpxchg16b " __percpu_arg(1), X86_FEATURE_CX16) \
+ "setz %0" \
+ : "=a" (__ret), "+m" (pcp1) \
+ : "b" (__n1), "c" (__n2), \
+ "a" (__o1), "d" (__o2) \
+ : "memory", "rsi"); \
__ret; \
})

--- a/arch/x86/lib/Makefile
+++ b/arch/x86/lib/Makefile
@@ -61,8 +61,9 @@ ifeq ($(CONFIG_X86_32),y)
lib-y += strstr_32.o
lib-y += string_32.o
lib-y += memmove_32.o
+ lib-y += cmpxchg8b_emu.o
ifneq ($(CONFIG_X86_CMPXCHG64),y)
- lib-y += cmpxchg8b_emu.o atomic64_386_32.o
+ lib-y += atomic64_386_32.o
endif
else
obj-y += iomap_copy_64.o
--- a/arch/x86/lib/cmpxchg16b_emu.S
+++ b/arch/x86/lib/cmpxchg16b_emu.S
@@ -1,47 +1,54 @@
/* SPDX-License-Identifier: GPL-2.0-only */
#include <linux/linkage.h>
#include <asm/percpu.h>
+#include <asm/processor-flags.h>

.text

/*
+ * Emulate 'cmpxchg16b %gs:(%rsi)'
+ *
* 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
+ *
+ * Notably this is not LOCK prefixed and is not safe against NMIs
*/
SYM_FUNC_START(this_cpu_cmpxchg16b_emu)

-#
-# Emulate 'cmpxchg16b %gs:(%rsi)' except we return the result in %al not
-# via the ZF. Caller will access %al to get result.
-#
-# Note that this is only useful for a cpuops operation. Meaning that we
-# do *not* have a fully atomic operation but just an operation that is
-# *atomic* on a single cpu (as provided by the this_cpu_xx class of
-# macros).
-#
pushfq
cli

- cmpq PER_CPU_VAR((%rsi)), %rax
- jne .Lnot_same
- cmpq PER_CPU_VAR(8(%rsi)), %rdx
- jne .Lnot_same
+ /* if (*ptr == old) */
+ cmpq PER_CPU_VAR(0(%rsi)), %rax
+ jne .Lnot_same
+ cmpq PER_CPU_VAR(8(%rsi)), %rdx
+ jne .Lnot_same
+
+ /* *ptr = new */
+ movq %rbx, PER_CPU_VAR(0(%rsi))
+ movq %rcx, PER_CPU_VAR(8(%rsi))

- movq %rbx, PER_CPU_VAR((%rsi))
- movq %rcx, PER_CPU_VAR(8(%rsi))
+ /* set ZF in EFLAGS to indicate success */
+ orl $X86_EFLAGS_ZF, (%rsp)

popfq
- mov $1, %al
RET

.Lnot_same:
+ /* *ptr != old */
+
+ /* old = *ptr */
+ movq PER_CPU_VAR(0(%rsi)), %rax
+ movq PER_CPU_VAR(8(%rsi)), %rdx
+
+ /* clear ZF in EFLAGS to indicate failure */
+ andl $(~X86_EFLAGS_ZF), (%rsp)
+
popfq
- xor %al,%al
RET

SYM_FUNC_END(this_cpu_cmpxchg16b_emu)
--- a/arch/x86/lib/cmpxchg8b_emu.S
+++ b/arch/x86/lib/cmpxchg8b_emu.S
@@ -2,10 +2,16 @@

#include <linux/linkage.h>
#include <asm/export.h>
+#include <asm/percpu.h>
+#include <asm/processor-flags.h>

.text

+#ifndef CONFIG_X86_CMPXCHG64
+
/*
+ * Emulate 'cmpxchg8b (%esi)' on UP
+ *
* Inputs:
* %esi : memory location to compare
* %eax : low 32 bits of old value
@@ -15,32 +21,65 @@
*/
SYM_FUNC_START(cmpxchg8b_emu)

-#
-# Emulate 'cmpxchg8b (%esi)' on UP except we don't
-# set the whole ZF thing (caller will just compare
-# eax:edx with the expected value)
-#
pushfl
cli

- cmpl (%esi), %eax
- jne .Lnot_same
- cmpl 4(%esi), %edx
- jne .Lhalf_same
+ cmpl 0(%esi), %eax
+ jne .Lnot_same
+ cmpl 4(%esi), %edx
+ jne .Lnot_same
+
+ movl %ebx, 0(%esi)
+ movl %ecx, 4(%esi)

- movl %ebx, (%esi)
- movl %ecx, 4(%esi)
+ orl $X86_EFLAGS_ZF, (%esp)

popfl
RET

.Lnot_same:
- movl (%esi), %eax
-.Lhalf_same:
- movl 4(%esi), %edx
+ movl 0(%esi), %eax
+ movl 4(%esi), %edx
+
+ andl $(~X86_EFLAGS_ZF), (%esp)

popfl
RET

SYM_FUNC_END(cmpxchg8b_emu)
EXPORT_SYMBOL(cmpxchg8b_emu)
+
+#endif
+
+#ifndef CONFIG_UML
+
+SYM_FUNC_START(this_cpu_cmpxchg8b_emu)
+
+ pushfl
+ cli
+
+ cmpl PER_CPU_VAR(0(%esi)), %eax
+ jne .Lnot_same2
+ cmpl PER_CPU_VAR(4(%esi)), %edx
+ jne .Lnot_same2
+
+ movl %ebx, PER_CPU_VAR(0(%esi))
+ movl %ecx, PER_CPU_VAR(4(%esi))
+
+ orl $X86_EFLAGS_ZF, (%esp)
+
+ popfl
+ RET
+
+.Lnot_same2:
+ movl PER_CPU_VAR(0(%esi)), %eax
+ movl PER_CPU_VAR(4(%esi)), %edx
+
+ andl $(~X86_EFLAGS_ZF), (%esp)
+
+ popfl
+ RET
+
+SYM_FUNC_END(this_cpu_cmpxchg8b_emu)
+
+#endif
--- a/include/asm-generic/percpu.h
+++ b/include/asm-generic/percpu.h
@@ -350,6 +350,25 @@ do { \
#endif
#endif

+#ifndef raw_cpu_try_cmpxchg64
+#ifdef raw_cpu_cmpxchg64
+#define raw_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ __cpu_fallback_try_cmpxchg(pcp, ovalp, nval, raw_cpu_cmpxchg64)
+#else
+#define raw_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#endif
+#ifndef raw_cpu_try_cmpxchg128
+#ifdef raw_cpu_cmpxchg128
+#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ __cpu_fallback_try_cmpxchg(pcp, ovalp, nval, raw_cpu_cmpxchg128)
+#else
+#define raw_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ raw_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#endif
+
#ifndef raw_cpu_cmpxchg_1
#define raw_cpu_cmpxchg_1(pcp, oval, nval) \
raw_cpu_generic_cmpxchg(pcp, oval, nval)
@@ -367,6 +386,15 @@ do { \
raw_cpu_generic_cmpxchg(pcp, oval, nval)
#endif

+#ifndef raw_cpu_cmpxchg64
+#define raw_cpu_cmpxchg64(pcp, oval, nval) \
+ raw_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
+#ifndef raw_cpu_cmpxchg128
+#define raw_cpu_cmpxchg128(pcp, oval, nval) \
+ raw_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
+
#ifndef raw_cpu_cmpxchg_double_1
#define raw_cpu_cmpxchg_double_1(pcp1, pcp2, oval1, oval2, nval1, nval2) \
raw_cpu_generic_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2)
@@ -512,6 +540,25 @@ do { \
#endif
#endif

+#ifndef this_cpu_try_cmpxchg64
+#ifdef this_cpu_cmpxchg64
+#define this_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ __cpu_fallback_try_cmpxchg(pcp, ovalp, nval, this_cpu_cmpxchg64)
+#else
+#define this_cpu_try_cmpxchg64(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#endif
+#ifndef this_cpu_try_cmpxchg128
+#ifdef this_cpu_cmpxchg128
+#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ __cpu_fallback_try_cmpxchg(pcp, ovalp, nval, this_cpu_cmpxchg128)
+#else
+#define this_cpu_try_cmpxchg128(pcp, ovalp, nval) \
+ this_cpu_generic_try_cmpxchg(pcp, ovalp, nval)
+#endif
+#endif
+
#ifndef this_cpu_cmpxchg_1
#define this_cpu_cmpxchg_1(pcp, oval, nval) \
this_cpu_generic_cmpxchg(pcp, oval, nval)
@@ -529,6 +576,15 @@ do { \
this_cpu_generic_cmpxchg(pcp, oval, nval)
#endif

+#ifndef this_cpu_cmpxchg64
+#define this_cpu_cmpxchg64(pcp, oval, nval) \
+ this_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
+#ifndef this_cpu_cmpxchg128
+#define this_cpu_cmpxchg128(pcp, oval, nval) \
+ this_cpu_generic_cmpxchg(pcp, oval, nval)
+#endif
+
#ifndef this_cpu_cmpxchg_double_1
#define this_cpu_cmpxchg_double_1(pcp1, pcp2, oval1, oval2, nval1, nval2) \
this_cpu_generic_cmpxchg_double(pcp1, pcp2, oval1, oval2, nval1, nval2)