[PATCH v2 4/7] arm64: add 'runtime constant' support

[Jimmy Tran <jtoantran@google.com>]

From: Linus Torvalds <torvalds@linux-foundation.org>

commit 94a2bc0f611cd9fa4d26e4679bf7ea4b01b12d56 upstream.

This implements the runtime constant infrastructure for arm64, allowing
the dcache d_hash() function to be generated using as a constant for
hash table address followed by shift by a constant of the hash index.

[ Fixed up to deal with the big-endian case as per Mark Rutland ]

Cc: <stable@vger.kernel.org> # 6.10.x: e60cc61: vfs: dcache: move hashlen_hash() from callers into d_hash()
Cc: <stable@vger.kernel.org> # 6.10.x: e782985: runtime constants: add default dummy infrastructure
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Jimmy Tran <jtoantran@google.com>
---
 arch/arm64/include/asm/runtime-const.h | 92 ++++++++++++++++++++++++++
 arch/arm64/kernel/vmlinux.lds.S        |  3 +
 2 files changed, 95 insertions(+)
 create mode 100644 arch/arm64/include/asm/runtime-const.h

diff --git a/arch/arm64/include/asm/runtime-const.h b/arch/arm64/include/asm/runtime-const.h
new file mode 100644
index 0000000000000..81faccb54e95d
--- /dev/null
+++ b/arch/arm64/include/asm/runtime-const.h
@@ -0,0 +1,92 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_RUNTIME_CONST_H
+#define _ASM_RUNTIME_CONST_H
+
+#include <asm/cacheflush.h>
+
+/* Sigh. You can still run arm64 in BE mode */
+#include <asm/byteorder.h>
+
+#define runtime_const_ptr(sym) ({				\
+	typeof(sym) __ret;					\
+	asm_inline("1:\t"					\
+		"movz %0, #0xcdef\n\t"				\
+		"movk %0, #0x89ab, lsl #16\n\t"			\
+		"movk %0, #0x4567, lsl #32\n\t"			\
+		"movk %0, #0x0123, lsl #48\n\t"			\
+		".pushsection runtime_ptr_" #sym ",\"a\"\n\t"	\
+		".long 1b - .\n\t"				\
+		".popsection"					\
+		 : "=r" (__ret));					\
+	__ret; })
+
+#define runtime_const_shift_right_32(val, sym) ({		\
+	unsigned long __ret;					\
+	asm_inline("1:\t"					\
+		"lsr %w0,%w1,#12\n\t"				\
+		".pushsection runtime_shift_" #sym ",\"a\"\n\t"	\
+		".long 1b - .\n\t"				\
+		".popsection"					\
+		 : "=r" (__ret)					\
+		 : "r" (0u+(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)
+
+/* 16-bit immediate for wide move (movz and movk) in bits 5..20 */
+static inline void __runtime_fixup_16(__le32 *p, unsigned int val)
+{
+	u32 insn = le32_to_cpu(*p);
+
+	insn &= 0xffe0001f;
+	insn |= (val & 0xffff) << 5;
+	*p = cpu_to_le32(insn);
+}
+
+static inline void __runtime_fixup_caches(void *where, unsigned int insns)
+{
+	unsigned long va = (unsigned long)where;
+
+	caches_clean_inval_pou(va, va + 4*insns);
+}
+
+static inline void __runtime_fixup_ptr(void *where, unsigned long val)
+{
+	__le32 *p = lm_alias(where);
+
+	__runtime_fixup_16(p, val);
+	__runtime_fixup_16(p+1, val >> 16);
+	__runtime_fixup_16(p+2, val >> 32);
+	__runtime_fixup_16(p+3, val >> 48);
+	__runtime_fixup_caches(where, 4);
+}
+
+/* Immediate value is 6 bits starting at bit #16 */
+static inline void __runtime_fixup_shift(void *where, unsigned long val)
+{
+	__le32 *p = lm_alias(where);
+	u32 insn = le32_to_cpu(*p);
+
+	insn &= 0xffc0ffff;
+	insn |= (val & 63) << 16;
+	*p = cpu_to_le32(insn);
+	__runtime_fixup_caches(where, 1);
+}
+
+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
diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
index d4353741f331e..f1719116592da 100644
--- a/arch/arm64/kernel/vmlinux.lds.S
+++ b/arch/arm64/kernel/vmlinux.lds.S
@@ -265,6 +265,9 @@ SECTIONS
 		EXIT_DATA
 	}
 
+	RUNTIME_CONST(shift, d_hash_shift)
+	RUNTIME_CONST(ptr, dentry_hashtable)
+
 	PERCPU_SECTION(L1_CACHE_BYTES)
 	HYPERVISOR_PERCPU_SECTION
 
-- 
2.50.1.470.g6ba607880d-goog