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[2001:1ae9:1c2:4c00:20f:c6b4:1e57:7965]) by smtp.gmail.com with ESMTPSA id a18-20020adfe5d2000000b002be505ab59asm14229155wrn.97.2023.02.24.08.26.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 24 Feb 2023 08:26:38 -0800 (PST) From: Andrew Jones To: linux-riscv@lists.infradead.org, kvm-riscv@lists.infradead.org, devicetree@vger.kernel.org Cc: 'Conor Dooley ' , 'Paul Walmsley ' , 'Palmer Dabbelt ' , 'Sudip Mukherjee ' , 'Ben Dooks ' , 'Atish Patra ' , 'Albert Ou ' , 'Anup Patel ' , 'Krzysztof Kozlowski ' , 'Rob Herring ' , 'Jisheng Zhang ' , 'Heiko Stuebner ' Subject: [PATCH v6 5/8] RISC-V: cpufeatures: Put the upper 16 bits of patch ID to work Date: Fri, 24 Feb 2023 17:26:28 +0100 Message-Id: <20230224162631.405473-6-ajones@ventanamicro.com> X-Mailer: git-send-email 2.39.1 In-Reply-To: <20230224162631.405473-1-ajones@ventanamicro.com> References: <20230224162631.405473-1-ajones@ventanamicro.com> MIME-Version: 1.0 Content-type: text/plain Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org cpufeature IDs are consecutive integers starting at 26, so a 32-bit patch ID allows an aircraft carrier load of feature IDs. Repurposing the upper 16 bits still leaves a boat load of feature IDs and gains 16 bits which may be used to control patching on a per patch-site basis. This will be initially used in Zicboz's application to clear_page(), as Zicboz's block size must also be considered. In that case, the upper 16-bit value's role will be to convey the maximum block size which the Zicboz clear_page() implementation supports. cpufeature patch sites which need to check for the existence or absence of other cpufeatures may also be able to make use of this. Signed-off-by: Andrew Jones Reviewed-by: Conor Dooley --- arch/riscv/include/asm/alternative.h | 4 +++ arch/riscv/kernel/cpufeature.c | 37 +++++++++++++++++++++++++--- 2 files changed, 37 insertions(+), 4 deletions(-) diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h index c8dea9e94310..58ccd2f8cab7 100644 --- a/arch/riscv/include/asm/alternative.h +++ b/arch/riscv/include/asm/alternative.h @@ -13,10 +13,14 @@ #ifdef CONFIG_RISCV_ALTERNATIVE #include +#include #include #include #include +#define PATCH_ID_CPUFEATURE_ID(p) lower_16_bits(p) +#define PATCH_ID_CPUFEATURE_VALUE(p) upper_16_bits(p) + #define RISCV_ALTERNATIVES_BOOT 0 /* alternatives applied during regular boot */ #define RISCV_ALTERNATIVES_MODULE 1 /* alternatives applied during module-init */ #define RISCV_ALTERNATIVES_EARLY_BOOT 2 /* alternatives applied before mmu start */ diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c index 538779d03311..d424cd76beb1 100644 --- a/arch/riscv/kernel/cpufeature.c +++ b/arch/riscv/kernel/cpufeature.c @@ -274,12 +274,35 @@ void __init riscv_fill_hwcap(void) } #ifdef CONFIG_RISCV_ALTERNATIVE +/* + * Alternative patch sites consider 48 bits when determining when to patch + * the old instruction sequence with the new. These bits are broken into a + * 16-bit vendor ID and a 32-bit patch ID. A non-zero vendor ID means the + * patch site is for an erratum, identified by the 32-bit patch ID. When + * the vendor ID is zero, the patch site is for a cpufeature. cpufeatures + * further break down patch ID into two 16-bit numbers. The lower 16 bits + * are the cpufeature ID and the upper 16 bits are used for a value specific + * to the cpufeature and patch site. If the upper 16 bits are zero, then it + * implies no specific value is specified. cpufeatures that want to control + * patching on a per-site basis will provide non-zero values and implement + * checks here. The checks return true when patching should be done, and + * false otherwise. + */ +static bool riscv_cpufeature_patch_check(u16 id, u16 value) +{ + if (!value) + return true; + + return false; +} + void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end, unsigned int stage) { struct alt_entry *alt; void *oldptr, *altptr; + u16 id, value; if (stage == RISCV_ALTERNATIVES_EARLY_BOOT) return; @@ -287,13 +310,19 @@ void __init_or_module riscv_cpufeature_patch_func(struct alt_entry *begin, for (alt = begin; alt < end; alt++) { if (alt->vendor_id != 0) continue; - if (alt->patch_id >= RISCV_ISA_EXT_MAX) { - WARN(1, "This extension id:%d is not in ISA extension list", - alt->patch_id); + + id = PATCH_ID_CPUFEATURE_ID(alt->patch_id); + + if (id >= RISCV_ISA_EXT_MAX) { + WARN(1, "This extension id:%d is not in ISA extension list", id); continue; } - if (!__riscv_isa_extension_available(NULL, alt->patch_id)) + if (!__riscv_isa_extension_available(NULL, id)) + continue; + + value = PATCH_ID_CPUFEATURE_VALUE(alt->patch_id); + if (!riscv_cpufeature_patch_check(id, value)) continue; oldptr = ALT_OLD_PTR(alt);