x86 boot: only pick up additional EFI memmap if add_efi_memmap flag

Applies on top of the previous patch:
x86 boot: add code to add BIOS provided EFI memory entries to kernel

Instead of always adding EFI memory map entries (if present) to the
memory map after initially finding either E820 BIOS memory map entries
and/or kernel command line memmap entries, -instead- only add such
additional EFI memory map entries if the kernel boot option:

add_efi_memmap

is specified.

Requiring this 'add_efi_memmap' option is backward compatible with
kernels that didn't load such additional EFI memory map entries in
the first place, and it doesn't override a configuration that tries
to replace all E820 or EFI BIOS memory map entries with ones given
entirely on the kernel command line.

Signed-off-by: Paul Jackson <[e-mail]>
Cc: "Yinghai Lu" <[e-mail]>
Cc: "Jack Steiner" <[e-mail]>
Cc: "Mike Travis" <[e-mail]>
Cc: "Huang
Cc: Ying" <[e-mail]>
Cc: "Andi Kleen" <[e-mail]>
Cc: "Andrew Morton" <[e-mail]>
Cc: Paul Jackson <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

Documentation/kernel-parameters.txt

···
 	usbhid.mousepoll=
 			[USBHID] The interval which mice are to be polled at.
 
+	add_efi_memmap	[EFI; x86-32,X86-64] Include EFI memory map in
+			kernel's map of available physical RAM.
+
 	vdso=		[X86-32,SH,x86-64]
 			vdso=2: enable compat VDSO (default with COMPAT_VDSO)
 			vdso=1: enable VDSO (default)

Documentation/x86/x86_64/uefi.txt

···
   services.
 	noefi		turn off all EFI runtime services
 	reboot_type=k	turn off EFI reboot runtime service
+- If the EFI memory map has additional entries not in the E820 map,
+  you can include those entries in the kernels memory map of available
+  physical RAM by using the following kernel command line parameter.
+	add_efi_memmap	include EFI memory map of available physical RAM

arch/x86/kernel/efi.c

···
 }
 early_param("noefi", setup_noefi);
 
+int add_efi_memmap;
+EXPORT_SYMBOL(add_efi_memmap);
+
+static int __init setup_add_efi_memmap(char *arg)
+{
+	add_efi_memmap = 1;
+	return 0;
+}
+early_param("add_efi_memmap", setup_add_efi_memmap);
+
+
 static efi_status_t virt_efi_get_time(efi_time_t *tm, efi_time_cap_t *tc)
 {
 	return efi_call_virt2(get_time, tm, tc);
···
  * (zeropage) memory map.
  */
 
-static void __init add_efi_memmap(void)
+static void __init do_add_efi_memmap(void)
 {
 	void *p;
 
···
 	if (memmap.desc_size != sizeof(efi_memory_desc_t))
 		printk(KERN_WARNING "Kernel-defined memdesc"
 		       "doesn't match the one from EFI!\n");
-	add_efi_memmap();
+	if (add_efi_memmap)
+		do_add_efi_memmap();
 
 	/* Setup for EFI runtime service */
 	reboot_type = BOOT_EFI;