s390/sclp: do not use static sccbs

The sccbs for init/read/sdias/early have to be located below 2 GB, and
they are currently defined as a static buffer.

With a relocatable kernel that could reside at any place in memory, this
will no longer guarantee the location below 2 GB, so use a dynamic
GFP_DMA allocation instead.

The sclp_early_sccb buffer needs special handling, as it can be used
very early, and by both the decompressor and also the decompressed
kernel. Therefore, a fixed 4 KB buffer is introduced at 0x11000, the
former PARMAREA_END. The new PARMAREA_END is now 0x12000, and it is
renamed to HEAD_END, as it is rather the end of head.S and not the end
of the parmarea.

Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Reviewed-by: Philipp Rudo <prudo@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/machine_kexec_file.c

@@ -337,10 +337,8 @@ int arch_kexec_kernel_image_probe(struct kimage *image, void *buf,
 	 * load memory in head.S will be accessed, e.g. to register the next
 	 * command line. If the next kernel were smaller the current kernel
 	 * will panic at load.
-	 *
-	 * 0x11000 = sizeof(head.S)
 	 */
-	if (buf_len < 0x11000)
+	if (buf_len < HEAD_END)
 		return -ENOEXEC;
 
 	return kexec_image_probe_default(image, buf, buf_len);

arch/s390/kernel/setup.c

@@ -829,7 +829,7 @@ static void __init reserve_kernel(void)
 {
 	unsigned long start_pfn = PFN_UP(__pa(_end));
 
-	memblock_reserve(0, PARMAREA_END);
+	memblock_reserve(0, HEAD_END);
 	memblock_reserve((unsigned long)_stext, PFN_PHYS(start_pfn)
 			 - (unsigned long)_stext);
 }