x86/kexec: Fix a kexec_file_load() failure

Commit

b6664ba42f14 ("s390, kexec_file: drop arch_kexec_mem_walk()")

changed the behavior of kexec_locate_mem_hole(): it will try to allocate
free memory only when kbuf.mem is initialized to zero.

However, x86's kexec_file_load() implementation reuses a struct
kexec_buf allocated on the stack and its kbuf.mem member gets set by
each kexec_add_buffer() invocation.

The second kexec_add_buffer() will reuse the same kbuf but not
reinitialize kbuf.mem.

Therefore, explictily reset kbuf.mem each time in order for
kexec_locate_mem_hole() to locate a free memory region each time.

[ bp: massage commit message. ]

Fixes: b6664ba42f14 ("s390, kexec_file: drop arch_kexec_mem_walk()")
Signed-off-by: Dave Young <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Acked-by: Baoquan He <[e-mail]>
Cc: "Eric W. Biederman" <[e-mail]>
Cc: "H. Peter Anvin" <[e-mail]>
Cc: AKASHI Takahiro <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Cc: Ingo Molnar <[e-mail]>
Cc: Martin Schwidefsky <[e-mail]>
Cc: Philipp Rudo <[e-mail]>
Cc: Thomas Gleixner <[e-mail]>
Cc: Vivek Goyal <[e-mail]>
Cc: Yannik Sembritzki <[e-mail]>
Cc: Yi Wang <[e-mail]>
Cc: [e-mail]
Cc: x86-ml <[e-mail]>
Link: https://lkml.kernel.org/r/[e-mail]

arch/x86/kernel/crash.c

···
 
 	kbuf.memsz = kbuf.bufsz;
 	kbuf.buf_align = ELF_CORE_HEADER_ALIGN;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	ret = kexec_add_buffer(&kbuf);
 	if (ret) {
 		vfree((void *)image->arch.elf_headers);

arch/x86/kernel/kexec-bzimage64.c

···
 	kbuf.memsz = PAGE_ALIGN(header->init_size);
 	kbuf.buf_align = header->kernel_alignment;
 	kbuf.buf_min = MIN_KERNEL_LOAD_ADDR;
+	kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 	ret = kexec_add_buffer(&kbuf);
 	if (ret)
 		goto out_free_params;
···
 		kbuf.bufsz = kbuf.memsz = initrd_len;
 		kbuf.buf_align = PAGE_SIZE;
 		kbuf.buf_min = MIN_INITRD_LOAD_ADDR;
+		kbuf.mem = KEXEC_BUF_MEM_UNKNOWN;
 		ret = kexec_add_buffer(&kbuf);
 		if (ret)
 			goto out_free_params;