powerpc/kexec: Fix loading of kernel + initramfs with kexec_file_load()

Commit b6664ba ("s390, kexec_file: drop arch_kexec_mem_walk()")
changed kexec_add_buffer() to skip searching for a memory location if
kexec_buf.mem is already set, and use the address that is there.

In powerpc code we reuse a kexec_buf variable for loading both the
kernel and the initramfs by resetting some of the fields between those
uses, but not mem. This causes kexec_add_buffer() to try to load the
kernel at the same address where initramfs will be loaded, which is
naturally rejected:

  # kexec -s -l --initrd initramfs vmlinuz
  kexec_file_load failed: Invalid argument

Setting the mem field before every call to kexec_add_buffer() fixes
this regression.

Fixes: b6664ba ("s390, kexec_file: drop arch_kexec_mem_walk()")
Cc: stable@vger.kernel.org # v5.0+
Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Reviewed-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/kexec_elf_64.c

@@ -547,6 +547,7 @@ static int elf_exec_load(struct kimage *image, struct elfhdr *ehdr,
 		kbuf.memsz = phdr->p_memsz;
 		kbuf.buf_align = phdr->p_align;
 		kbuf.buf_min = phdr->p_paddr + base;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 		ret = kexec_add_buffer(&kbuf);
 		if (ret)
 			goto out;
@@ -581,7 +582,8 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
 	struct kexec_buf kbuf = { .image = image, .buf_min = 0,
 				  .buf_max = ppc64_rma_size };
 	struct kexec_buf pbuf = { .image = image, .buf_min = 0,
-				  .buf_max = ppc64_rma_size, .top_down = true };
+				  .buf_max = ppc64_rma_size, .top_down = true,
+				  .mem = KEXEC_BUF_MEM_UNKNOWN };
 
 	ret = build_elf_exec_info(kernel_buf, kernel_len, &ehdr, &elf_info);
 	if (ret)
@@ -606,6 +608,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
 		kbuf.bufsz = kbuf.memsz = initrd_len;
 		kbuf.buf_align = PAGE_SIZE;
 		kbuf.top_down = false;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 		ret = kexec_add_buffer(&kbuf);
 		if (ret)
 			goto out;
@@ -638,6 +641,7 @@ static void *elf64_load(struct kimage *image, char *kernel_buf,
 	kbuf.bufsz = kbuf.memsz = fdt_size;
 	kbuf.buf_align = PAGE_SIZE;
 	kbuf.top_down = true;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	ret = kexec_add_buffer(&kbuf);
 	if (ret)
 		goto out;