LoongArch: Make KASAN usable for variable cpu_vabits

commit 3c25226 upstream.

Currently, KASAN on LoongArch assume the CPU VA bits is 48, which is
true for Loongson-3 series, but not for Loongson-2 series (only 40 or
lower), this patch fix that issue and make KASAN usable for variable
cpu_vabits.

Solution is very simple: Just define XRANGE_SHADOW_SHIFT which means
valid address length from VA_BITS to min(cpu_vabits, VA_BITS).

Cc: stable@vger.kernel.org
Signed-off-by: Kanglong Wang <wangkanglong@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: chenhuacai

arch/loongarch/include/asm/kasan.h

@@ -16,7 +16,7 @@
 #define XRANGE_SHIFT (48)
 
 /* Valid address length */
-#define XRANGE_SHADOW_SHIFT	(PGDIR_SHIFT + PAGE_SHIFT - 3)
+#define XRANGE_SHADOW_SHIFT	min(cpu_vabits, VA_BITS)
 /* Used for taking out the valid address */
 #define XRANGE_SHADOW_MASK	GENMASK_ULL(XRANGE_SHADOW_SHIFT - 1, 0)
 /* One segment whole address space size */