[PATCH v3 03/11] riscv: Implement cmpxchg8/16() using Zabha

Alexandre Ghiti
2024-07-17T06:23:11Z

This adds runtime support for Zabha in cmpxchg8/16() operations.

Note that in the absence of Zacas support in the toolchain, CAS
instructions from Zabha won't be used.

Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>
---
arch/riscv/Kconfig | 17 ++++++++++++++++
arch/riscv/Makefile | 3 +++
arch/riscv/include/asm/cmpxchg.h | 33 ++++++++++++++++++++++++++++++--
arch/riscv/include/asm/hwcap.h | 1 +
arch/riscv/kernel/cpufeature.c | 1 +
5 files changed, 53 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 1caaedec88c7..d3b0f92f92da 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -596,6 +596,23 @@ config RISCV_ISA_V_PREEMPTIVE
preemption. Enabling this config will result in higher memory
consumption due to the allocation of per-task's kernel Vector context.

+config TOOLCHAIN_HAS_ZABHA
+ bool
+ default y
+ depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zabha)
+ depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zabha)
+ depends on AS_HAS_OPTION_ARCH
+
+config RISCV_ISA_ZABHA
+ bool "Zabha extension support for atomic byte/halfword operations"
+ depends on TOOLCHAIN_HAS_ZABHA
+ default y
+ help
+ Enable the use of the Zabha ISA-extension to implement kernel
+ byte/halfword atomic memory operations when it is detected at boot.
+
+ If you don't know what to do here, say Y.
+
config TOOLCHAIN_HAS_ZACAS
bool
default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index 9fd13d7a9cc6..78dcaaeebf4e 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -88,6 +88,9 @@ riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZIHINTPAUSE) := $(riscv-march-y)_zihintpause
# Check if the toolchain supports Zacas
riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZACAS) := $(riscv-march-y)_zacas

+# Check if the toolchain supports Zabha
+riscv-march-$(CONFIG_TOOLCHAIN_HAS_ZABHA) := $(riscv-march-y)_zabha
+
# Remove F,D,V from isa string for all. Keep extensions between "fd" and "v" by
# matching non-v and non-multi-letter extensions out with the filter ([^v_]*)
KBUILD_CFLAGS += -march=$(shell echo $(riscv-march-y) | sed -E 's/(rv32ima|rv64ima)fd([^v_]*)v?/\1\2/')
diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index 5d38153e2f13..c86722a101d0 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -105,8 +105,30 @@
* indicated by comparing RETURN with OLD.
*/

-#define __arch_cmpxchg_masked(sc_sfx, prepend, append, r, p, o, n) \
+#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, prepend, append, r, p, o, n) \
({ \
+ __label__ no_zabha_zacas, end; \
+ \
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) && \
+ IS_ENABLED(CONFIG_RISCV_ISA_ZACAS)) { \
+ asm goto(ALTERNATIVE("j %[no_zabha_zacas]", "nop", 0, \
+ RISCV_ISA_EXT_ZABHA, 1) \
+ : : : : no_zabha_zacas); \
+ asm goto(ALTERNATIVE("j %[no_zabha_zacas]", "nop", 0, \
+ RISCV_ISA_EXT_ZACAS, 1) \
+ : : : : no_zabha_zacas); \
+ \
+ __asm__ __volatile__ ( \
+ prepend \
+ " amocas" cas_sfx " %0, %z2, %1\n" \
+ append \
+ : "+&r" (r), "+A" (*(p)) \
+ : "rJ" (n) \
+ : "memory"); \
+ goto end; \
+ } \
+ \
+no_zabha_zacas:; \
u32 *__ptr32b = (u32 *)((ulong)(p) & ~0x3); \
ulong __s = ((ulong)(p) & (0x4 - sizeof(*p))) * BITS_PER_BYTE; \
ulong __mask = GENMASK(((sizeof(*p)) * BITS_PER_BYTE) - 1, 0) \
@@ -133,6 +155,8 @@
: "memory"); \
\
r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
+ \
+end:; \
})

#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \
@@ -180,8 +204,13 @@ end:; \
\
switch (sizeof(*__ptr)) { \
case 1: \
+ __arch_cmpxchg_masked(sc_sfx, ".b" sc_sfx, \
+ prepend, append, \
+ __ret, __ptr, __old, __new); \
+ break; \
case 2: \
- __arch_cmpxchg_masked(sc_sfx, prepend, append, \
+ __arch_cmpxchg_masked(sc_sfx, ".h" sc_sfx, \
+ prepend, append, \
__ret, __ptr, __old, __new); \
break; \
case 4: \
diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index e17d0078a651..f71ddd2ca163 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -81,6 +81,7 @@
#define RISCV_ISA_EXT_ZTSO 72
#define RISCV_ISA_EXT_ZACAS 73
#define RISCV_ISA_EXT_XANDESPMU 74
+#define RISCV_ISA_EXT_ZABHA 75

#define RISCV_ISA_EXT_XLINUXENVCFG 127

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 5ef48cb20ee1..c125d82c894b 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -257,6 +257,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
__RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
__RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
__RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
+ __RISCV_ISA_EXT_DATA(zabha, RISCV_ISA_EXT_ZABHA),
__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
__RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
__RISCV_ISA_EXT_DATA(zfhmin, RISCV_ISA_EXT_ZFHMIN),
--
2.39.2