arm64/insn: introduce aarch64_insn_gen_{nop|branch_imm}() helper functions

This is copied from Linux 4.7, and the initial commit
that put this in is 5c5bf25d4f7a950382f94fc120a5818197b48fe9
"arm64: introduce aarch64_insn_gen_{nop|branch_imm}() helper functions"

This lays the groundwork for Livepatch to generate the
trampoline to jump to the new replacement function.
Also allows us to NOP the callsites.

Acked-by: Julien Grall <julien.grall@arm.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

--
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Julien Grall <julien.grall@arm.com>

RFC: First submission
v1: The full copy of insn_gen_branch instead of just the code to make branch
v2: Added Julien's Ack.
    Remove the duplicate paragraph in the commit message.

xen/arch/arm/arm64/insn.c

@@ -157,6 +157,67 @@ u32 __kprobes aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
 	return insn;
 }
 
+static inline long branch_imm_common(unsigned long pc, unsigned long addr,
+				     long range)
+{
+	long offset;
+
+	if ((pc & 0x3) || (addr & 0x3)) {
+		pr_err("%s: A64 instructions must be word aligned\n", __func__);
+		return range;
+	}
+
+	offset = ((long)addr - (long)pc);
+
+	if (offset < -range || offset >= range) {
+		pr_err("%s: offset out of range\n", __func__);
+		return range;
+	}
+
+	return offset;
+}
+
+u32 __kprobes aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
+					  enum aarch64_insn_branch_type type)
+{
+	u32 insn;
+	long offset;
+
+	/*
+	 * B/BL support [-128M, 128M) offset
+	 * ARM64 virtual address arrangement guarantees all kernel and module
+	 * texts are within +/-128M.
+	 */
+	offset = branch_imm_common(pc, addr, SZ_128M);
+	if (offset >= SZ_128M)
+		return AARCH64_BREAK_FAULT;
+
+	switch (type) {
+	case AARCH64_INSN_BRANCH_LINK:
+		insn = aarch64_insn_get_bl_value();
+		break;
+	case AARCH64_INSN_BRANCH_NOLINK:
+		insn = aarch64_insn_get_b_value();
+		break;
+	default:
+		pr_err("%s: unknown branch encoding %d\n", __func__, type);
+		return AARCH64_BREAK_FAULT;
+	}
+
+	return aarch64_insn_encode_immediate(AARCH64_INSN_IMM_26, insn,
+					     offset >> 2);
+}
+
+u32 __kprobes aarch64_insn_gen_hint(enum aarch64_insn_hint_op op)
+{
+	return aarch64_insn_get_hint_value() | op;
+}
+
+u32 __kprobes aarch64_insn_gen_nop(void)
+{
+	return aarch64_insn_gen_hint(AARCH64_INSN_HINT_NOP);
+}
+
 /*
  * Decode the imm field of a branch, and return the byte offset as a
  * signed value (so it can be used when computing a new branch

xen/include/asm-arm/arm64/insn.h

@@ -23,6 +23,15 @@
 #include <xen/types.h>
 #include <xen/stdbool.h>
 
+enum aarch64_insn_hint_op {
+	AARCH64_INSN_HINT_NOP	= 0x0 << 5,
+	AARCH64_INSN_HINT_YIELD	= 0x1 << 5,
+	AARCH64_INSN_HINT_WFE	= 0x2 << 5,
+	AARCH64_INSN_HINT_WFI	= 0x3 << 5,
+	AARCH64_INSN_HINT_SEV	= 0x4 << 5,
+	AARCH64_INSN_HINT_SEVL	= 0x5 << 5,
+};
+
 enum aarch64_insn_imm_type {
 	AARCH64_INSN_IMM_ADR,
 	AARCH64_INSN_IMM_26,
@@ -38,6 +47,14 @@ enum aarch64_insn_imm_type {
 	AARCH64_INSN_IMM_MAX
 };
 
+enum aarch64_insn_branch_type {
+	AARCH64_INSN_BRANCH_NOLINK,
+	AARCH64_INSN_BRANCH_LINK,
+	AARCH64_INSN_BRANCH_RETURN,
+	AARCH64_INSN_BRANCH_COMP_ZERO,
+	AARCH64_INSN_BRANCH_COMP_NONZERO,
+};
+
 #define	__AARCH64_INSN_FUNCS(abbr, mask, val)	\
 static always_inline bool_t aarch64_insn_is_##abbr(u32 code) \
 { return (code & (mask)) == (val); } \
@@ -51,6 +68,7 @@ __AARCH64_INSN_FUNCS(cbnz,	0x7F000000, 0x35000000)
 __AARCH64_INSN_FUNCS(tbz,	0x7F000000, 0x36000000)
 __AARCH64_INSN_FUNCS(tbnz,	0x7F000000, 0x37000000)
 __AARCH64_INSN_FUNCS(bcond,	0xFF000010, 0x54000000)
+__AARCH64_INSN_FUNCS(hint,	0xFFFFF01F, 0xD503201F)
 
 bool aarch64_insn_is_branch_imm(u32 insn);
 
@@ -61,6 +79,11 @@ u32 aarch64_insn_encode_immediate(enum aarch64_insn_imm_type type,
 s32 aarch64_get_branch_offset(u32 insn);
 u32 aarch64_set_branch_offset(u32 insn, s32 offset);
 
+u32 aarch64_insn_gen_branch_imm(unsigned long pc, unsigned long addr,
+				enum aarch64_insn_branch_type type);
+u32 aarch64_insn_gen_hint(enum aarch64_insn_hint_op op);
+u32 aarch64_insn_gen_nop(void);
+
 /* Wrapper for common code */
 static inline bool insn_is_branch_imm(u32 insn)
 {