powerpc/sstep: Emulate prefixed instructions only when CPU_FTR_ARCH_31 is set

Unconditional emulation of prefixed instructions will allow
emulation of them on Power10 predecessors which might cause
issues. Restrict that.

Fixes: 3920742b ("powerpc sstep: Add support for prefixed fixed-point arithmetic")
Fixes: 50b80a12 ("powerpc sstep: Add support for prefixed load/stores")
Signed-off-by: Balamuruhan S <bala24@linux.ibm.com>
Signed-off-by: Ravi Bangoria <ravi.bangoria@linux.ibm.com>
Reviewed-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-by: Daniel Axtens <dja@axtens.net>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20201011050908.72173-2-ravi.bangoria@linux.ibm.com

arch/powerpc/lib/sstep.c

@@ -1346,6 +1346,9 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 	switch (opcode) {
 #ifdef __powerpc64__
 	case 1:
+		if (!cpu_has_feature(CPU_FTR_ARCH_31))
+			return -1;
+
 		prefix_r = GET_PREFIX_R(word);
 		ra = GET_PREFIX_RA(suffix);
 		rd = (suffix >> 21) & 0x1f;
@@ -2733,6 +2736,9 @@ int analyse_instr(struct instruction_op *op, const struct pt_regs *regs,
 		}
 		break;
 	case 1: /* Prefixed instructions */
+		if (!cpu_has_feature(CPU_FTR_ARCH_31))
+			return -1;
+
 		prefix_r = GET_PREFIX_R(word);
 		ra = GET_PREFIX_RA(suffix);
 		op->update_reg = ra;