x86/kexec: Do not reserve EFI setup_data in the kexec e820 table

The e820 table for the kexec kernel unconditionally marks setup_data as
reserved because the second kernel can reuse setup_data passed by the
1st kernel's boot loader, for example SETUP_PCI marked regions like PCI
BIOS, etc.

SETUP_EFI types, however, are used by kexec itself to enable EFI in the
2nd kernel. Thus, it is pointless to add this type of setup_data to the
kexec e820 table as reserved.

IOW, what happens is this:

  -  1st physical boot: no SETUP_EFI.

  - kexec loads a new kernel and prepares a SETUP_EFI setup_data blob, then
  reboots the machine.

  - 2nd kernel sees SETUP_EFI, reserves it both in the e820 and in the
  kexec e820 table.

  - If another kexec load is executed, it prepares a new SETUP_EFI blob and
  then reboots the machine into the new kernel.

  5. The 3rd kexec-ed kernel has two SETUP_EFI ranges reserved. And so on...

Thus skip SETUP_EFI while reserving setup_data in the e820_table_kexec
table because it is not needed.

 [ bp: Heavily massage commit message, shorten line and improve comment. ]
Signed-off-by: Dave Young <dyoung@redhat.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20200212110424.GA2938@dhcp-128-65.nay.redhat.com

arch/x86/kernel/e820.c

@@ -999,7 +999,15 @@ void __init e820__reserve_setup_data(void)
 	while (pa_data) {
 		data = early_memremap(pa_data, sizeof(*data));
 		e820__range_update(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
-		e820__range_update_kexec(pa_data, sizeof(*data)+data->len, E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
+
+		/*
+		 * SETUP_EFI is supplied by kexec and does not need to be
+		 * reserved.
+		 */
+		if (data->type != SETUP_EFI)
+			e820__range_update_kexec(pa_data,
+						 sizeof(*data) + data->len,
+						 E820_TYPE_RAM, E820_TYPE_RESERVED_KERN);
 
 		if (data->type == SETUP_INDIRECT &&
 		    ((struct setup_indirect *)data->data)->type != SETUP_INDIRECT) {