[PATCH v4 05/13] riscv: Implement cmpxchg8/16() using Zabha

Alexandre Ghiti
2024-07-31T07:29:15Z

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 | 18 ++++++++
arch/riscv/Makefile | 3 ++
arch/riscv/include/asm/cmpxchg.h | 78 ++++++++++++++++++++------------
arch/riscv/include/asm/hwcap.h | 1 +
arch/riscv/kernel/cpufeature.c | 1 +
5 files changed, 72 insertions(+), 29 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index d955c64d50c2..212ec2aab389 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -613,6 +613,24 @@ config RISCV_ISA_ZAWRS
use of these instructions in the kernel when the Zawrs extension is
detected at boot.

+config TOOLCHAIN_HAS_ZABHA
+ bool
+ default y
+ depends on !64BIT || $(cc-option,-mabi=lp64 -march=rv64ima_zabha)
+ depends on !32BIT || $(cc-option,-mabi=ilp32 -march=rv32ima_zabha)
+ depends on AS_HAS_OPTION_ARCH
+
+config RISCV_ISA_ZABHA
+ bool "Zabha extension support for atomic byte/halfword operations"
+ depends on TOOLCHAIN_HAS_ZABHA
+ depends on RISCV_ALTERNATIVE
+ default y
+ help
+ Enable the use of the Zabha ISA-extension to implement kernel
+ byte/halfword atomic memory operations when it is detected at boot.
+
+ If you don't know what to do here, say Y.
+
config TOOLCHAIN_HAS_ZACAS
bool
default y
diff --git a/arch/riscv/Makefile b/arch/riscv/Makefile
index f1788131d5fe..f6dc5ba7c526 100644
--- a/arch/riscv/Makefile
+++ b/arch/riscv/Makefile
@@ -85,6 +85,9 @@ endif
# Check if the toolchain supports Zacas
riscv-march-$(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 c626fe0d08ae..ebcd4a30ae60 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -108,34 +108,49 @@
* indicated by comparing RETURN with OLD.
*/

-#define __arch_cmpxchg_masked(sc_sfx, prepend, append, r, p, o, n) \
-({ \
- 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) \
- << __s; \
- ulong __newx = (ulong)(n) << __s; \
- ulong __oldx = (ulong)(o) << __s; \
- ulong __retx; \
- ulong __rc; \
- \
- __asm__ __volatile__ ( \
- prepend \
- "0: lr.w %0, %2\n" \
- " and %1, %0, %z5\n" \
- " bne %1, %z3, 1f\n" \
- " and %1, %0, %z6\n" \
- " or %1, %1, %z4\n" \
- " sc.w" sc_sfx " %1, %1, %2\n" \
- " bnez %1, 0b\n" \
- append \
- "1:\n" \
- : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b)) \
- : "rJ" ((long)__oldx), "rJ" (__newx), \
- "rJ" (__mask), "rJ" (~__mask) \
- : "memory"); \
- \
- r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
+#define __arch_cmpxchg_masked(sc_sfx, cas_sfx, prepend, append, r, p, o, n) \
+({ \
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) && \
+ IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) && \
+ riscv_has_extension_unlikely(RISCV_ISA_EXT_ZABHA) && \
+ riscv_has_extension_unlikely(RISCV_ISA_EXT_ZACAS)) { \
+ r = o; \
+ \
+ __asm__ __volatile__ ( \
+ prepend \
+ " amocas" cas_sfx " %0, %z2, %1\n" \
+ append \
+ : "+&r" (r), "+A" (*(p)) \
+ : "rJ" (n) \
+ : "memory"); \
+ } else { \
+ 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) \
+ << __s; \
+ ulong __newx = (ulong)(n) << __s; \
+ ulong __oldx = (ulong)(o) << __s; \
+ ulong __retx; \
+ ulong __rc; \
+ \
+ __asm__ __volatile__ ( \
+ prepend \
+ "0: lr.w %0, %2\n" \
+ " and %1, %0, %z5\n" \
+ " bne %1, %z3, 1f\n" \
+ " and %1, %0, %z6\n" \
+ " or %1, %1, %z4\n" \
+ " sc.w" sc_sfx " %1, %1, %2\n" \
+ " bnez %1, 0b\n" \
+ append \
+ "1:\n" \
+ : "=&r" (__retx), "=&r" (__rc), "+A" (*(__ptr32b)) \
+ : "rJ" ((long)__oldx), "rJ" (__newx), \
+ "rJ" (__mask), "rJ" (~__mask) \
+ : "memory"); \
+ \
+ r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
+ } \
})

#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \
@@ -177,8 +192,13 @@
\
switch (sizeof(*__ptr)) { \
case 1: \
+ __arch_cmpxchg_masked(sc_cas_sfx, ".b" sc_cas_sfx, \
+ prepend, append, \
+ __ret, __ptr, __old, __new); \
+ break; \
case 2: \
- __arch_cmpxchg_masked(sc_cas_sfx, prepend, append, \
+ __arch_cmpxchg_masked(sc_cas_sfx, ".h" sc_cas_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 5a0bd27fd11a..f5d53251c947 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -92,6 +92,7 @@
#define RISCV_ISA_EXT_ZCF 83
#define RISCV_ISA_EXT_ZCMOP 84
#define RISCV_ISA_EXT_ZAWRS 85
+#define RISCV_ISA_EXT_ZABHA 86

#define RISCV_ISA_EXT_XLINUXENVCFG 127

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 8f20607adb40..2a608056c89c 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -322,6 +322,7 @@ 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(zimop, RISCV_ISA_EXT_ZIMOP),
+ __RISCV_ISA_EXT_DATA(zabha, RISCV_ISA_EXT_ZABHA),
__RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
__RISCV_ISA_EXT_DATA(zawrs, RISCV_ISA_EXT_ZAWRS),
__RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
--
2.39.2