riscv: Support BUG() in kernel module

The kernel module is loaded into vmalloc region which is located below
to the PAGE_OFFSET. Hence the condition, pc < PAGE_OFFSET, in the
is_valid_bugaddr() will filter out all trap exceptions triggered
by kernel module. To support BUG() in kernel module, the condition is
changed to pc < VMALLOC_START.

Signed-off-by: Vincent Chen <vincentc@andestech.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/traps.c

@@ -156,7 +156,7 @@ int is_valid_bugaddr(unsigned long pc)
 {
 	bug_insn_t insn;
 
-	if (pc < PAGE_OFFSET)
+	if (pc < VMALLOC_START)
 		return 0;
 	if (probe_kernel_address((bug_insn_t *)pc, insn))
 		return 0;