Re: [PATCH v2 03/10] riscv: Implement cmpxchg8/16() using Zabha

Andrea Parri
2024-06-27T11:53:34Z

> -#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_zacas, zabha, end; \
> + \
> + if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> + asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
> + RISCV_ISA_EXT_ZACAS, 1) \
> + : : : : no_zacas); \
> + asm goto(ALTERNATIVE("nop", "j %[zabha]", 0, \
> + RISCV_ISA_EXT_ZABHA, 1) \
> + : : : : zabha); \
> + } \
> + \
> +no_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 +145,19 @@
> : "memory"); \
> \
> r = (__typeof__(*(p)))((__retx & __mask) >> __s); \
> + goto end; \
> + \
> +zabha: \
> + if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
> + __asm__ __volatile__ ( \
> + prepend \
> + " amocas" cas_sfx " %0, %z2, %1\n" \
> + append \
> + : "+&r" (r), "+A" (*(p)) \
> + : "rJ" (n) \
> + : "memory"); \
> + } \
> +end:; \
> })

I admit that I found this all quite difficult to read; IIUC, this is
missing an IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) check. How about adding
such a check under the zabha: label (replacing/in place of the second
IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) check) and moving the corresponding
asm goto statement there, perhaps as follows? (on top of this patch)

Also, the patch presents the first occurrence of RISCV_ISA_EXT_ZABHA;
perhaps worth moving the hwcap/cpufeature changes from patch #6 here?

Andrea

diff --git a/arch/riscv/include/asm/cmpxchg.h b/arch/riscv/include/asm/cmpxchg.h
index b9a3fdcec919..3c913afec150 100644
--- a/arch/riscv/include/asm/cmpxchg.h
+++ b/arch/riscv/include/asm/cmpxchg.h
@@ -110,15 +110,12 @@
__label__ no_zacas, zabha, end; \
\
if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
- asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
- RISCV_ISA_EXT_ZACAS, 1) \
- : : : : no_zacas); \
asm goto(ALTERNATIVE("nop", "j %[zabha]", 0, \
RISCV_ISA_EXT_ZABHA, 1) \
: : : : zabha); \
} \
\
-no_zacas:; \
+no_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) \
@@ -148,16 +145,20 @@ no_zacas:; \
goto end; \
\
zabha: \
- if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA)) { \
- __asm__ __volatile__ ( \
- prepend \
- " amocas" cas_sfx " %0, %z2, %1\n" \
- append \
- : "+&r" (r), "+A" (*(p)) \
- : "rJ" (n) \
- : "memory"); \
+ if (IS_ENABLED(CONFIG_RISCV_ISA_ZAZAS)) { \
+ asm goto(ALTERNATIVE("j %[no_zacas]", "nop", 0, \
+ RISCV_ISA_EXT_ZACAS, 1) \
+ : : : : no_zacas); \
} \
-end:; \
+ \
+ __asm__ __volatile__ ( \
+ prepend \
+ " amocas" cas_sfx " %0, %z2, %1\n" \
+ append \
+ : "+&r" (r), "+A" (*(p)) \
+ : "rJ" (n) \
+ : "memory"); \
+end: \
})

#define __arch_cmpxchg(lr_sfx, sc_cas_sfx, prepend, append, r, p, co, o, n) \