MIPS: Add defs & probing of BadInstr[P] registers

The optional CP0_BadInstr and CP0_BadInstrP registers are written with
the encoding of the instruction that caused a synchronous exception to
occur, and the prior branch instruction if in a delay slot.

These will be useful for instruction emulation in KVM, and especially
for VZ support where reading guest virtual memory is a bit more awkward.

Add CPU option numbers and cpu_has_* definitions to indicate the
presence of each registers, and add code to probe for them using bits in
the CP0_Config3 register.

[ralf@linux-mips.org: resolve merge conflict.]

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/13224/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/cpu-features.h

@@ -442,4 +442,12 @@
 # define cpu_has_ebase_wg	(cpu_data[0].options & MIPS_CPU_EBASE_WG)
 #endif
 
+#ifndef cpu_has_badinstr
+# define cpu_has_badinstr	(cpu_data[0].options & MIPS_CPU_BADINSTR)
+#endif
+
+#ifndef cpu_has_badinstrp
+# define cpu_has_badinstrp	(cpu_data[0].options & MIPS_CPU_BADINSTRP)
+#endif
+
 #endif /* __ASM_CPU_FEATURES_H */

arch/mips/include/asm/cpu.h

@@ -405,6 +405,8 @@ enum cpu_type_enum {
 #define MIPS_CPU_LDPTE		MBIT_ULL(41)	/* CPU has ldpte/lddir instructions */
 #define MIPS_CPU_MVH		MBIT_ULL(42)	/* CPU supports MFHC0/MTHC0 */
 #define MIPS_CPU_EBASE_WG	MBIT_ULL(43)	/* CPU has EBase.WG */
+#define MIPS_CPU_BADINSTR	MBIT_ULL(44)	/* CPU has BadInstr register */
+#define MIPS_CPU_BADINSTRP	MBIT_ULL(45)	/* CPU has BadInstrP register */
 
 /*
  * CPU ASE encodings

arch/mips/include/asm/mipsregs.h

@@ -1248,6 +1248,9 @@ do {									\
 #define read_c0_badvaddr()	__read_ulong_c0_register($8, 0)
 #define write_c0_badvaddr(val)	__write_ulong_c0_register($8, 0, val)
 
+#define read_c0_badinstr()	__read_32bit_c0_register($8, 1)
+#define read_c0_badinstrp()	__read_32bit_c0_register($8, 2)
+
 #define read_c0_count()		__read_32bit_c0_register($9, 0)
 #define write_c0_count(val)	__write_32bit_c0_register($9, 0, val)
 

arch/mips/kernel/cpu-probe.c

@@ -714,6 +714,10 @@ static inline unsigned int decode_config3(struct cpuinfo_mips *c)
 		c->ases |= MIPS_ASE_VZ;
 	if (config3 & MIPS_CONF3_SC)
 		c->options |= MIPS_CPU_SEGMENTS;
+	if (config3 & MIPS_CONF3_BI)
+		c->options |= MIPS_CPU_BADINSTR;
+	if (config3 & MIPS_CONF3_BP)
+		c->options |= MIPS_CPU_BADINSTRP;
 	if (config3 & MIPS_CONF3_MSA)
 		c->ases |= MIPS_ASE_MSA;
 	if (config3 & MIPS_CONF3_PW) {