From d25f256332cc795b0fe16ba541fe0c05f0eb2c59 Mon Sep 17 00:00:00 2001 From: Andrew Jones Date: Fri, 24 Feb 2023 17:26:28 +0100 Subject: [PATCH] RISC-V: cpufeatures: Put the upper 16 bits of patch ID to work 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 Link: https://lore.kernel.org/r/20230224162631.405473-6-ajones@ventanamicro.com Signed-off-by: Palmer Dabbelt --- 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); -- 2.11.0