MIPS: traps: 64bit kernels should read CP0_EBase 64bit

When reading the CP0_EBase register containing the WG (write gate) bit,
the ebase variable should be set to the full value of the register, i.e.
on a 64-bit kernel the full 64-bit width of the register via
read_cp0_ebase_64(), and on a 32-bit kernel the full 32-bit width
including bits 31:30 which may be writeable.

Signed-off-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: Matt Redfearn <matt.redfearn@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14148/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/kernel/traps.c

@@ -2215,8 +2215,17 @@ void __init trap_init(void)
 	} else {
 		ebase = CAC_BASE;
 
-		if (cpu_has_mips_r2_r6)
-			ebase += (read_c0_ebase() & 0x3ffff000);
+		if (cpu_has_mips_r2_r6) {
+			if (cpu_has_ebase_wg) {
+#ifdef CONFIG_64BIT
+				ebase = (read_c0_ebase_64() & ~0xfff);
+#else
+				ebase = (read_c0_ebase() & ~0xfff);
+#endif
+			} else {
+				ebase += (read_c0_ebase() & 0x3ffff000);
+			}
+		}
 	}
 
 	if (cpu_has_mmips) {