From 6216182fb776ae546c5566f21976d116c8650cee Mon Sep 17 00:00:00 2001 From: Conor Dooley Date: Thu, 24 Oct 2024 11:19:40 +0100 Subject: [PATCH 1/2] RISC-V: clarify what some RISCV_ISA* config options do During some discussion on IRC yesterday and on Pu's bpf patch [1] I noticed that these RISCV_ISA* Kconfig options are not really clear about their implications. Many of these options have no impact on what userspace is allowed to do, for example an application can use Zbb regardless of whether or not the kernel does. Change the help text to try and clarify whether or not an option affects just the kernel, or also userspace. None of these options actually control whether or not an extension is detected dynamically as that's done regardless of Kconfig options, so drop any text that implies the option is required for dynamic detection, rewording them as "do x when y is detected". Link: https://lore.kernel.org/linux-riscv/20240328-ferocity-repose-c554f75a676c@spud/ [1] Reviewed-by: Andrew Jones Signed-off-by: Conor Dooley Reviewed-by: Charlie Jenkins Reviewed-by: Samuel Holland Link: https://lore.kernel.org/r/20241024-overdue-slogan-0b0f69d3da91@spud Signed-off-by: Alexandre Ghiti --- arch/riscv/Kconfig | 36 +++++++++++++++++++----------------- 1 file changed, 19 insertions(+), 17 deletions(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 62545946ecf4..278a38c94c5a 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -527,7 +527,8 @@ config RISCV_ISA_C help Adds "C" to the ISA subsets that the toolchain is allowed to emit when building Linux, which results in compressed instructions in the - Linux binary. + Linux binary. This option produces a kernel that will not run on + systems that do not support compressed instructions. If you don't know what to do here, say Y. @@ -537,8 +538,8 @@ config RISCV_ISA_SVNAPOT depends on RISCV_ALTERNATIVE default y help - Allow kernel to detect the Svnapot ISA-extension dynamically at boot - time and enable its usage. + Enable support for the Svnapot ISA-extension when it is detected + at boot. The Svnapot extension is used to mark contiguous PTEs as a range of contiguous virtual-to-physical translations for a naturally @@ -556,9 +557,8 @@ config RISCV_ISA_SVPBMT depends on RISCV_ALTERNATIVE default y help - Adds support to dynamically detect the presence of the Svpbmt - ISA-extension (Supervisor-mode: page-based memory types) and - enable its usage. + Add support for the Svpbmt ISA-extension (Supervisor-mode: + page-based memory types) in the kernel when it is detected at boot. The memory type for a page contains a combination of attributes that indicate the cacheability, idempotency, and ordering @@ -577,14 +577,15 @@ config TOOLCHAIN_HAS_V depends on AS_HAS_OPTION_ARCH config RISCV_ISA_V - bool "VECTOR extension support" + bool "Vector extension support" depends on TOOLCHAIN_HAS_V depends on FPU select DYNAMIC_SIGFRAME default y help - Say N here if you want to disable all vector related procedure - in the kernel. + Add support for the Vector extension when it is detected at boot. + When this option is disabled, neither the kernel nor userspace may + use vector procedures. If you don't know what to do here, say Y. @@ -667,8 +668,8 @@ config RISCV_ISA_ZBB depends on RISCV_ALTERNATIVE default y help - Adds support to dynamically detect the presence of the ZBB - extension (basic bit manipulation) and enable its usage. + Add support for enabling optimisations in the kernel when the + Zbb extension is detected at boot. The Zbb extension provides instructions to accelerate a number of bit-specific operations (count bit population, sign extending, @@ -707,9 +708,9 @@ config RISCV_ISA_ZICBOM select RISCV_DMA_NONCOHERENT select DMA_DIRECT_REMAP help - Adds support to dynamically detect the presence of the ZICBOM - extension (Cache Block Management Operations) and enable its - usage. + Add support for the Zicbom extension (Cache Block Management + Operations) and enable its use in the kernel when it is detected + at boot. The Zicbom extension can be used to handle for example non-coherent DMA support on devices that need it. @@ -722,7 +723,7 @@ config RISCV_ISA_ZICBOZ default y help Enable the use of the Zicboz extension (cbo.zero instruction) - when available. + in the kernel when it is detected at boot. The Zicboz extension is used for faster zeroing of memory. @@ -760,8 +761,9 @@ config FPU bool "FPU support" default y help - Say N here if you want to disable all floating-point related procedure - in the kernel. + Add support for floating point operations when an FPU is detected at + boot. When this option is disabled, neither the kernel nor userspace + may use the floating point unit. If you don't know what to do here, say Y. From 9343aaba1f256ff42730db5a61efc32a86149776 Mon Sep 17 00:00:00 2001 From: Conor Dooley Date: Thu, 24 Oct 2024 11:19:41 +0100 Subject: [PATCH 2/2] RISC-V: separate Zbb optimisations requiring and not requiring toolchain support It seems a bit ridiculous to require toolchain support for BPF to assemble Zbb instructions, so move the dependency on toolchain support for Zbb optimisations out of the Kconfig option and to the callsites. Zbb support has always depended on alternatives, so while adjusting the config options guarding optimisations, remove any checks for whether or not alternatives are enabled. Reviewed-by: Andrew Jones Signed-off-by: Conor Dooley Reviewed-by: Charlie Jenkins Reviewed-by: Samuel Holland Link: https://lore.kernel.org/r/20241024-chump-freebase-d26b6d81af33@spud Signed-off-by: Alexandre Ghiti --- arch/riscv/Kconfig | 4 ++-- arch/riscv/include/asm/arch_hweight.h | 6 +++--- arch/riscv/include/asm/bitops.h | 4 ++-- arch/riscv/include/asm/checksum.h | 3 +-- arch/riscv/lib/csum.c | 21 +++------------------ arch/riscv/lib/strcmp.S | 5 +++-- arch/riscv/lib/strlen.S | 5 +++-- arch/riscv/lib/strncmp.S | 5 +++-- 8 files changed, 20 insertions(+), 33 deletions(-) diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig index 278a38c94c5a..6ec7a500a25f 100644 --- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -664,12 +664,12 @@ config RISCV_ISA_ZBA config RISCV_ISA_ZBB bool "Zbb extension support for bit manipulation instructions" - depends on TOOLCHAIN_HAS_ZBB depends on RISCV_ALTERNATIVE default y help Add support for enabling optimisations in the kernel when the - Zbb extension is detected at boot. + Zbb extension is detected at boot. Some optimisations may + additionally depend on toolchain support for Zbb. The Zbb extension provides instructions to accelerate a number of bit-specific operations (count bit population, sign extending, diff --git a/arch/riscv/include/asm/arch_hweight.h b/arch/riscv/include/asm/arch_hweight.h index 613769b9cdc9..0e7cdbbec8ef 100644 --- a/arch/riscv/include/asm/arch_hweight.h +++ b/arch/riscv/include/asm/arch_hweight.h @@ -19,7 +19,7 @@ static __always_inline unsigned int __arch_hweight32(unsigned int w) { -#ifdef CONFIG_RISCV_ISA_ZBB +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1) : : : : legacy); @@ -50,7 +50,7 @@ static inline unsigned int __arch_hweight8(unsigned int w) #if BITS_PER_LONG == 64 static __always_inline unsigned long __arch_hweight64(__u64 w) { -# ifdef CONFIG_RISCV_ISA_ZBB +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) asm goto(ALTERNATIVE("j %l[legacy]", "nop", 0, RISCV_ISA_EXT_ZBB, 1) : : : : legacy); @@ -64,7 +64,7 @@ static __always_inline unsigned long __arch_hweight64(__u64 w) return w; legacy: -# endif +#endif return __sw_hweight64(w); } #else /* BITS_PER_LONG == 64 */ diff --git a/arch/riscv/include/asm/bitops.h b/arch/riscv/include/asm/bitops.h index fae152ea0508..410e2235d658 100644 --- a/arch/riscv/include/asm/bitops.h +++ b/arch/riscv/include/asm/bitops.h @@ -15,7 +15,7 @@ #include #include -#if !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) +#if !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE) #include #include #include @@ -175,7 +175,7 @@ static __always_inline int variable_fls(unsigned int x) variable_fls(x_); \ }) -#endif /* !defined(CONFIG_RISCV_ISA_ZBB) || defined(NO_ALTERNATIVE) */ +#endif /* !(defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB)) || defined(NO_ALTERNATIVE) */ #include #include diff --git a/arch/riscv/include/asm/checksum.h b/arch/riscv/include/asm/checksum.h index 88e6f1499e88..da378856f1d5 100644 --- a/arch/riscv/include/asm/checksum.h +++ b/arch/riscv/include/asm/checksum.h @@ -49,8 +49,7 @@ static inline __sum16 ip_fast_csum(const void *iph, unsigned int ihl) * ZBB only saves three instructions on 32-bit and five on 64-bit so not * worth checking if supported without Alternatives. */ - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) { + if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) { unsigned long fold_temp; asm goto(ALTERNATIVE("j %l[no_zbb]", "nop", 0, diff --git a/arch/riscv/lib/csum.c b/arch/riscv/lib/csum.c index 7fb12c59e571..9408f50ca59a 100644 --- a/arch/riscv/lib/csum.c +++ b/arch/riscv/lib/csum.c @@ -40,12 +40,7 @@ __sum16 csum_ipv6_magic(const struct in6_addr *saddr, uproto = (__force unsigned int)htonl(proto); sum += uproto; - /* - * Zbb support saves 4 instructions, so not worth checking without - * alternatives if supported - */ - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) { + if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) { unsigned long fold_temp; /* @@ -157,12 +152,7 @@ do_csum_with_alignment(const unsigned char *buff, int len) csum = do_csum_common(ptr, end, data); #ifdef CC_HAS_ASM_GOTO_TIED_OUTPUT - /* - * Zbb support saves 6 instructions, so not worth checking without - * alternatives if supported - */ - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) { + if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) { unsigned long fold_temp; /* @@ -244,12 +234,7 @@ do_csum_no_alignment(const unsigned char *buff, int len) end = (const unsigned long *)(buff + len); csum = do_csum_common(ptr, end, data); - /* - * Zbb support saves 6 instructions, so not worth checking without - * alternatives if supported - */ - if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && - IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) { + if (IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) { unsigned long fold_temp; /* diff --git a/arch/riscv/lib/strcmp.S b/arch/riscv/lib/strcmp.S index 57a5c0066231..65027e742af1 100644 --- a/arch/riscv/lib/strcmp.S +++ b/arch/riscv/lib/strcmp.S @@ -8,7 +8,8 @@ /* int strcmp(const char *cs, const char *ct) */ SYM_FUNC_START(strcmp) - ALTERNATIVE("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB) + __ALTERNATIVE_CFG("nop", "j strcmp_zbb", 0, RISCV_ISA_EXT_ZBB, + IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) /* * Returns @@ -43,7 +44,7 @@ SYM_FUNC_START(strcmp) * The code was published as part of the bitmanip manual * in Appendix A. */ -#ifdef CONFIG_RISCV_ISA_ZBB +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) strcmp_zbb: .option push diff --git a/arch/riscv/lib/strlen.S b/arch/riscv/lib/strlen.S index 962983b73251..eb4d2b7ed22b 100644 --- a/arch/riscv/lib/strlen.S +++ b/arch/riscv/lib/strlen.S @@ -8,7 +8,8 @@ /* int strlen(const char *s) */ SYM_FUNC_START(strlen) - ALTERNATIVE("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB) + __ALTERNATIVE_CFG("nop", "j strlen_zbb", 0, RISCV_ISA_EXT_ZBB, + IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) /* * Returns @@ -33,7 +34,7 @@ SYM_FUNC_START(strlen) /* * Variant of strlen using the ZBB extension if available */ -#ifdef CONFIG_RISCV_ISA_ZBB +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) strlen_zbb: #ifdef CONFIG_CPU_BIG_ENDIAN diff --git a/arch/riscv/lib/strncmp.S b/arch/riscv/lib/strncmp.S index 7b2d0ff9ed6c..062000c468c8 100644 --- a/arch/riscv/lib/strncmp.S +++ b/arch/riscv/lib/strncmp.S @@ -8,7 +8,8 @@ /* int strncmp(const char *cs, const char *ct, size_t count) */ SYM_FUNC_START(strncmp) - ALTERNATIVE("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB, CONFIG_RISCV_ISA_ZBB) + __ALTERNATIVE_CFG("nop", "j strncmp_zbb", 0, RISCV_ISA_EXT_ZBB, + IS_ENABLED(CONFIG_RISCV_ISA_ZBB) && IS_ENABLED(CONFIG_TOOLCHAIN_HAS_ZBB)) /* * Returns @@ -46,7 +47,7 @@ SYM_FUNC_START(strncmp) /* * Variant of strncmp using the ZBB extension if available */ -#ifdef CONFIG_RISCV_ISA_ZBB +#if defined(CONFIG_RISCV_ISA_ZBB) && defined(CONFIG_TOOLCHAIN_HAS_ZBB) strncmp_zbb: .option push