arm64: insn: simplify insn group identification

The only code which needs to check for an entire instruction group is
the aarch64_insn_is_steppable() helper function used by kprobes, which
must not be instrumented, and only needs to check for the "Branch,
exception generation and system instructions" class.

Currently we have an out-of-line helper in insn.c which must be marked
as __kprobes, which indexes a table with some bits extracted from the
instruction. In aarch64_insn_is_steppable() we then need to compare the
result with an expected enum value.

It would be simpler to have a predicate for this, as with the other
aarch64_insn_is_*() helpers, which would be always inlined to prevent
inadvertent instrumentation, and would permit better code generation.

This patch adds a predicate function for this instruction group using
the existing __AARCH64_INSN_FUNCS() helpers, and removes the existing
out-of-line helper. As the only class we currently care about is the
branch+exception+sys class, I have only added helpers for this, and left
the other classes unimplemented for now.

There should be no functional change as a result of this patch.

Signed-off-by: Mark Rutland <[email protected]>
Cc: Catalin Marinas <[email protected]>
Cc: Joey Gouly <[email protected]>
Cc: Will Deacon <[email protected]>
Reviewed-by: Joey Gouly <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Will Deacon <[email protected]>

Author: Mark Rutland

arch/arm64/include/asm/insn.h

@@ -13,31 +13,6 @@
 #include <asm/insn-def.h>
 
 #ifndef __ASSEMBLY__
-/*
- * ARM Architecture Reference Manual for ARMv8 Profile-A, Issue A.a
- * Section C3.1 "A64 instruction index by encoding":
- * AArch64 main encoding table
- *  Bit position
- *   28 27 26 25	Encoding Group
- *   0  0  -  -		Unallocated
- *   1  0  0  -		Data processing, immediate
- *   1  0  1  -		Branch, exception generation and system instructions
- *   -  1  -  0		Loads and stores
- *   -  1  0  1		Data processing - register
- *   0  1  1  1		Data processing - SIMD and floating point
- *   1  1  1  1		Data processing - SIMD and floating point
- * "-" means "don't care"
- */
-enum aarch64_insn_encoding_class {
-	AARCH64_INSN_CLS_UNKNOWN,	/* UNALLOCATED */
-	AARCH64_INSN_CLS_SVE,		/* SVE instructions */
-	AARCH64_INSN_CLS_DP_IMM,	/* Data processing - immediate */
-	AARCH64_INSN_CLS_DP_REG,	/* Data processing - register */
-	AARCH64_INSN_CLS_DP_FPSIMD,	/* Data processing - SIMD and FP */
-	AARCH64_INSN_CLS_LDST,		/* Loads and stores */
-	AARCH64_INSN_CLS_BR_SYS,	/* Branch, exception generation and
-					 * system instructions */
-};
 
 enum aarch64_insn_hint_cr_op {
 	AARCH64_INSN_HINT_NOP	= 0x0 << 5,
@@ -326,6 +301,23 @@ static __always_inline u32 aarch64_insn_get_##abbr##_value(void)	\
 	return (val);							\
 }
 
+/*
+ * ARM Architecture Reference Manual for ARMv8 Profile-A, Issue A.a
+ * Section C3.1 "A64 instruction index by encoding":
+ * AArch64 main encoding table
+ *  Bit position
+ *   28 27 26 25	Encoding Group
+ *   0  0  -  -		Unallocated
+ *   1  0  0  -		Data processing, immediate
+ *   1  0  1  -		Branch, exception generation and system instructions
+ *   -  1  -  0		Loads and stores
+ *   -  1  0  1		Data processing - register
+ *   0  1  1  1		Data processing - SIMD and floating point
+ *   1  1  1  1		Data processing - SIMD and floating point
+ * "-" means "don't care"
+ */
+__AARCH64_INSN_FUNCS(class_branch_sys,	0x1c000000, 0x14000000)
+
 __AARCH64_INSN_FUNCS(adr,	0x9F000000, 0x10000000)
 __AARCH64_INSN_FUNCS(adrp,	0x9F000000, 0x90000000)
 __AARCH64_INSN_FUNCS(prfm,	0x3FC00000, 0x39800000)

arch/arm64/kernel/probes/decode-insn.c

@@ -24,7 +24,7 @@ static bool __kprobes aarch64_insn_is_steppable(u32 insn)
 	 * currently safe. Lastly, MSR instructions can do any number of nasty
 	 * things we can't handle during single-stepping.
 	 */
-	if (aarch64_get_insn_class(insn) == AARCH64_INSN_CLS_BR_SYS) {
+	if (aarch64_insn_is_class_branch_sys(insn)) {
 		if (aarch64_insn_is_branch(insn) ||
 		    aarch64_insn_is_msr_imm(insn) ||
 		    aarch64_insn_is_msr_reg(insn) ||

arch/arm64/lib/insn.c

@@ -20,30 +20,6 @@
 #define AARCH64_INSN_N_BIT	BIT(22)
 #define AARCH64_INSN_LSL_12	BIT(22)
 
-static const int aarch64_insn_encoding_class[] = {
-	AARCH64_INSN_CLS_UNKNOWN,
-	AARCH64_INSN_CLS_UNKNOWN,
-	AARCH64_INSN_CLS_SVE,
-	AARCH64_INSN_CLS_UNKNOWN,
-	AARCH64_INSN_CLS_LDST,
-	AARCH64_INSN_CLS_DP_REG,
-	AARCH64_INSN_CLS_LDST,
-	AARCH64_INSN_CLS_DP_FPSIMD,
-	AARCH64_INSN_CLS_DP_IMM,
-	AARCH64_INSN_CLS_DP_IMM,
-	AARCH64_INSN_CLS_BR_SYS,
-	AARCH64_INSN_CLS_BR_SYS,
-	AARCH64_INSN_CLS_LDST,
-	AARCH64_INSN_CLS_DP_REG,
-	AARCH64_INSN_CLS_LDST,
-	AARCH64_INSN_CLS_DP_FPSIMD,
-};
-
-enum aarch64_insn_encoding_class __kprobes aarch64_get_insn_class(u32 insn)
-{
-	return aarch64_insn_encoding_class[(insn >> 25) & 0xf];
-}
-
 static int __kprobes aarch64_get_imm_shift_mask(enum aarch64_insn_imm_type type,
 						u32 *maskp, int *shiftp)
 {