s390: Add runtime constant support

Implement the runtime constant infrastructure for s390, 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.

This is the s390 variant of commit 94a2bc0f ("arm64: add 'runtime
constant' support") and commit e3c92e81 ("runtime constants: add
x86 architecture support").
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Acked-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/runtime-const.h

+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _ASM_S390_RUNTIME_CONST_H
+#define _ASM_S390_RUNTIME_CONST_H
+
+#include <linux/uaccess.h>
+
+#define runtime_const_ptr(sym)					\
+({								\
+	typeof(sym) __ret;					\
+								\
+	asm_inline(						\
+		"0:	iihf	%[__ret],%[c1]\n"		\
+		"	iilf	%[__ret],%[c2]\n"		\
+		".pushsection runtime_ptr_" #sym ",\"a\"\n"	\
+		".long 0b - .\n"				\
+		".popsection"					\
+		: [__ret] "=d" (__ret)				\
+		: [c1] "i" (0x01234567UL),			\
+		  [c2] "i" (0x89abcdefUL));			\
+	__ret;							\
+})
+
+#define runtime_const_shift_right_32(val, sym)			\
+({								\
+	unsigned int __ret = (val);				\
+								\
+	asm_inline(						\
+		"0:	srl	%[__ret],12\n"			\
+		".pushsection runtime_shift_" #sym ",\"a\"\n"	\
+		".long 0b - .\n"				\
+		".popsection"					\
+		: [__ret] "+d" (__ret));			\
+	__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)
+
+/* 32-bit immediate for iihf and iilf in bits in I2 field */
+static inline void __runtime_fixup_32(u32 *p, unsigned int val)
+{
+	s390_kernel_write(p, &val, sizeof(val));
+}
+
+static inline void __runtime_fixup_ptr(void *where, unsigned long val)
+{
+	__runtime_fixup_32(where + 2, val >> 32);
+	__runtime_fixup_32(where + 8, val);
+}
+
+/* Immediate value is lower 12 bits of D2 field of srl */
+static inline void __runtime_fixup_shift(void *where, unsigned long val)
+{
+	u32 insn = *(u32 *)where;
+
+	insn &= 0xfffff000;
+	insn |= (val & 63);
+	s390_kernel_write(where, &insn, 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_S390_RUNTIME_CONST_H */

arch/s390/kernel/vmlinux.lds.S

@@ -190,6 +190,9 @@ SECTIONS
 	. = ALIGN(PAGE_SIZE);
 	INIT_DATA_SECTION(0x100)
 
+	RUNTIME_CONST(shift, d_hash_shift)
+	RUNTIME_CONST(ptr, dentry_hashtable)
+
 	PERCPU_SECTION(0x100)
 
 	. = ALIGN(PAGE_SIZE);