riscv: kexec: Align the kexeced kernel entry

The current riscv boot protocol requires 2MB alignment for RV64
and 4MB alignment for RV32.

In KEXEC_FILE path, the elf_find_pbase() function should align
the kexeced kernel entry according to the requirement, otherwise
the kexeced kernel would silently BUG at the setup_vm().

Fixes: 8acea455fafa ("RISC-V: Support for kexec_file on panic")
Signed-off-by: Song Shuai <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Palmer Dabbelt <[e-mail]>

arch/riscv/kernel/elf_kexec.c

···
 	kbuf.image = image;
 	kbuf.buf_min = lowest_paddr;
 	kbuf.buf_max = ULONG_MAX;
-	kbuf.buf_align = PAGE_SIZE;
+
+	/*
+	 * Current riscv boot protocol requires 2MB alignment for
+	 * RV64 and 4MB alignment for RV32
+	 *
+	 */
+	kbuf.buf_align = PMD_SIZE;
 	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	kbuf.memsz = ALIGN(kernel_len, PAGE_SIZE);
 	kbuf.top_down = false;