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Message-Id: <20250128-runtime_const_riscv-v3-1-11922989e2d3@rivosinc.com>
Date: Tue, 28 Jan 2025 12:06:08 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>, Ard Biesheuvel <ardb@...nel.org>,
Ben Dooks <ben.dooks@...ethink.co.uk>,
Pasha Bouzarjomehri <pasha@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH v3] riscv: Add runtime constant support
Implement the runtime constant infrastructure for riscv. Use this
infrastructure to generate constants to be used by the d_hash()
function.
This is the riscv variant of commit 94a2bc0f611c ("arm64: add 'runtime
constant' support") and commit e3c92e81711d ("runtime constants: add
x86 architecture support").
Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
Ard brought this to my attention in this patch [1].
[1] https://lore.kernel.org/lkml/CAMj1kXE4DJnwFejNWQu784GvyJO=aGNrzuLjSxiowX_e7nW8QA@mail.gmail.com/
---
Changes in v3:
- Leverage "pack" instruction for runtime_const_ptr() to reduce hot path
by 3 instructions if Zbkb is supported. Suggested by Pasha Bouzarjomehri (pasha@...osinc.com)
- Link to v2: https://lore.kernel.org/r/20250127-runtime_const_riscv-v2-1-95ae7cf97a39@rivosinc.com
Changes in v2:
- Treat instructions as __le32 and do proper conversions (Ben)
- Link to v1: https://lore.kernel.org/r/20250127-runtime_const_riscv-v1-1-795b023ea20b@rivosinc.com
---
arch/riscv/include/asm/runtime-const.h | 194 +++++++++++++++++++++++++++++++++
arch/riscv/kernel/vmlinux.lds.S | 3 +
2 files changed, 197 insertions(+)
diff --git a/arch/riscv/include/asm/runtime-const.h b/arch/riscv/include/asm/runtime-const.h
new file mode 100644
index 0000000000000000000000000000000000000000..0ecbe6967013900781b0b1048d4622f676b64076
--- /dev/null
+++ b/arch/riscv/include/asm/runtime-const.h
@@ -0,0 +1,194 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RISCV_RUNTIME_CONST_H
+#define _ASM_RISCV_RUNTIME_CONST_H
+
+#include <asm/alternative.h>
+#include <asm/cacheflush.h>
+#include <asm/text-patching.h>
+#include <linux/uaccess.h>
+
+#ifdef CONFIG_32BIT
+#define runtime_const_ptr(sym) \
+({ \
+ typeof(sym) __ret, __tmp; \
+ asm_inline("1:\t" \
+ ".option push" \
+ ".option norvc" \
+ "lui %[__ret],0x89abd\n\t" \
+ "addi %[__ret],-0x211\n\t" \
+ ".option pop" \
+ ".pushsection runtime_ptr_" #sym ",\"a\"\n\t" \
+ ".long 1b - .\n\t" \
+ ".popsection" \
+ : [__ret] "=r" (__ret)); \
+ __ret; \
+})
+#else
+/*
+ * Loading 64-bit constants into a register from immediates is a non-trivial
+ * task on riscv64. To get it somewhat performant, load 32 bits into two
+ * different registers and then combine the results.
+ *
+ * If the processor supports the Zbkb extension, we can combine the final
+ * "slli,slli,srli,add" into the single "pack" instruction. If the processor
+ * doesn't support Zbkb but does support the Zbb extension, we can
+ * combine the final "slli,srli,add" into one instruction "add.uw".
+ */
+#define runtime_const_ptr(sym) \
+({ \
+ typeof(sym) __ret, __tmp; \
+ asm_inline("1:\t" \
+ ".option push\n\t" \
+ ".option norvc\n\t" \
+ "lui %[__ret],0x89abd\n\t" \
+ "lui %[__tmp],0x1234\n\t" \
+ "addiw %[__ret],%[__ret],-0x211\n\t" \
+ "addiw %[__tmp],%[__tmp],0x567\n\t" \
+ ALTERNATIVE_2( \
+ "slli %[__tmp],%[__tmp],32\n\t" \
+ "slli %[__ret],%[__ret],32\n\t" \
+ "srli %[__ret],%[__ret],32\n\t" \
+ "add %[__ret],%[__ret],%[__tmp]\n\t", \
+ ".option push\n\t" \
+ ".option arch,+zba\n\t" \
+ "slli %[__tmp],%[__tmp],32\n\t" \
+ "add.uw %[__ret],%[__ret],%[__tmp]\n\t" \
+ "nop\n\t" \
+ "nop\n\t" \
+ ".option pop\n\t", \
+ 0, RISCV_ISA_EXT_ZBA, 1, \
+ ".option push\n\t" \
+ ".option arch,+zbkb\n\t" \
+ "pack %[__ret],%[__ret],%[__tmp]\n\t" \
+ "nop\n\t" \
+ "nop\n\t" \
+ "nop\n\t" \
+ ".option pop\n\t", \
+ 0, RISCV_ISA_EXT_ZBKB, 1 \
+ ) \
+ ".option pop\n\t" \
+ ".pushsection runtime_ptr_" #sym ",\"a\"\n\t" \
+ ".long 1b - .\n\t" \
+ ".popsection" \
+ : [__ret] "=r" (__ret), [__tmp] "=r" (__tmp)); \
+ __ret; \
+})
+#endif
+
+#ifdef CONFIG_32BIT
+#define SRLI "srli "
+#else
+#define SRLI "srliw "
+#endif
+
+#define runtime_const_shift_right_32(val, sym) \
+({ \
+ u32 __ret; \
+ asm_inline("1:\t" \
+ ".option push\n\t" \
+ ".option norvc\n\t" \
+ SRLI "%[__ret],%[__val],12\n\t" \
+ ".option pop\n\t" \
+ ".pushsection runtime_shift_" #sym ",\"a\"\n\t" \
+ ".long 1b - .\n\t" \
+ ".popsection" \
+ : [__ret] "=r" (__ret) \
+ : [__val] "r" (val)); \
+ __ret; \
+})
+
+#define runtime_const_init(type, sym) do { \
+ extern s32 __start_runtime_##type##_##sym[]; \
+ extern s32 __stop_runtime_##type##_##sym[]; \
+ \
+ runtime_const_fixup(__runtime_fixup_##type, \
+ (unsigned long)(sym), \
+ __start_runtime_##type##_##sym, \
+ __stop_runtime_##type##_##sym); \
+} while (0)
+
+static inline void __runtime_fixup_caches(void *where, unsigned int insns)
+{
+ /* On riscv there are currently only cache-wide flushes so va is ignored. */
+ __always_unused uintptr_t va = (uintptr_t)where;
+
+ flush_icache_range(va, va + 4*insns);
+}
+
+/*
+ * The 32-bit immediate is stored in a lui+addi pairing.
+ * lui holds the upper 20 bits of the immediate in the first 20 bits of the instruction.
+ * addi holds the lower 12 bits of the immediate in the first 12 bits of the instruction.
+ */
+static inline void __runtime_fixup_32(u32 *lui, u32 *addi, unsigned int val)
+{
+ unsigned int lower_immediate, upper_immediate;
+ u32 lui_insn = le32_to_cpu(*lui);
+ u32 addi_insn = le32_to_cpu(*addi);
+ __le32 addi_res, lui_res;
+
+ lower_immediate = sign_extend32(val, 11);
+ upper_immediate = (val - lower_immediate);
+
+ if (upper_immediate & 0xfffff000) {
+ /* replace upper 20 bits of lui with upper immediate */
+ lui_insn &= 0x00000fff;
+ lui_insn |= upper_immediate & 0xfffff000;
+ } else {
+ /* replace lui with nop if immediate is small enough to fit in addi */
+ lui_insn = 0x00000013;
+ }
+
+ if (lower_immediate & 0x00000fff) {
+ /* replace upper 12 bits of addi with lower 12 bits of val */
+ addi_insn &= 0x000fffff;
+ addi_insn |= (lower_immediate & 0x00000fff) << 20;
+ } else {
+ /* replace addi with nop if lower_immediate is empty */
+ addi_insn = 0x00000013;
+ }
+
+ addi_res = cpu_to_le32(addi_insn);
+ lui_res = cpu_to_le32(lui_insn);
+ patch_insn_write(addi, &addi_res, sizeof(addi_res));
+ patch_insn_write(lui, &lui_res, sizeof(lui_res));
+}
+
+static inline void __runtime_fixup_ptr(void *where, unsigned long val)
+{
+ if (IS_ENABLED(CONFIG_32BIT)) {
+ __runtime_fixup_32(where, where + 4, val);
+ __runtime_fixup_caches(where, 2);
+ } else {
+ __runtime_fixup_32(where, where + 8, val);
+ __runtime_fixup_32(where + 4, where + 12, val >> 32);
+ __runtime_fixup_caches(where, 4);
+ }
+}
+
+/*
+ * Replace the least significant 5 bits of the srli/srliw immediate that is
+ * located at bits 20-24
+ */
+static inline void __runtime_fixup_shift(void *where, unsigned long val)
+{
+ u32 insn = le32_to_cpu(*(__le32 *)where);
+ __le32 res;
+
+ insn &= 0xfe0fffff;
+ insn |= (val & 0b11111) << 20;
+
+ res = cpu_to_le32(insn);
+ patch_text_nosync(where, &res, sizeof(insn));
+}
+
+static inline void runtime_const_fixup(void (*fn)(void *, unsigned long),
+ unsigned long val, s32 *start, s32 *end)
+{
+ while (start < end) {
+ fn(*start + (void *)start, val);
+ start++;
+ }
+}
+
+#endif /* _ASM_RISCV_RUNTIME_CONST_H */
diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 002ca58dd998cb78b662837b5ebac988fb6c77bb..61bd5ba6680a786bf1db7dc37bf1acda0639b5c7 100644
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -97,6 +97,9 @@ SECTIONS
{
EXIT_DATA
}
+
+ RUNTIME_CONST_VARIABLES
+
PERCPU_SECTION(L1_CACHE_BYTES)
.rel.dyn : {
---
base-commit: ffd294d346d185b70e28b1a28abe367bbfe53c04
change-id: 20250123-runtime_const_riscv-6cd854ee2817
--
- Charlie
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