x86/setup: Call early_reserve_memory() earlier

Commit in Fixes introduced early_reserve_memory() to do all needed
initial memblock_reserve() calls in one function. Unfortunately, the call
of early_reserve_memory() is done too late for Xen dom0, as in some
cases a Xen hook called by e820__memory_setup() will need those memory
reservations to have happened already.

Move the call of early_reserve_memory() before the call of
e820__memory_setup() in order to avoid such problems.

Fixes: a799c2bd29 ("x86/setup: Consolidate early memory reservations")
Reported-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Tested-by: Marek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Tested-by: Nathan Chancellor <nathan@kernel.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20210920120421.29276-1-jgross@suse.com

arch/x86/kernel/setup.c

@@ -830,6 +830,20 @@ void __init setup_arch(char **cmdline_p)
 
 	x86_init.oem.arch_setup();
 
+	/*
+	 * Do some memory reservations *before* memory is added to memblock, so
+	 * memblock allocations won't overwrite it.
+	 *
+	 * After this point, everything still needed from the boot loader or
+	 * firmware or kernel text should be early reserved or marked not RAM in
+	 * e820. All other memory is free game.
+	 *
+	 * This call needs to happen before e820__memory_setup() which calls the
+	 * xen_memory_setup() on Xen dom0 which relies on the fact that those
+	 * early reservations have happened already.
+	 */
+	early_reserve_memory();
+
 	iomem_resource.end = (1ULL << boot_cpu_data.x86_phys_bits) - 1;
 	e820__memory_setup();
 	parse_setup_data();
@@ -876,18 +890,6 @@ void __init setup_arch(char **cmdline_p)
 
 	parse_early_param();
 
-	/*
-	 * Do some memory reservations *before* memory is added to
-	 * memblock, so memblock allocations won't overwrite it.
-	 * Do it after early param, so we could get (unlikely) panic from
-	 * serial.
-	 *
-	 * After this point everything still needed from the boot loader or
-	 * firmware or kernel text should be early reserved or marked not
-	 * RAM in e820. All other memory is free game.
-	 */
-	early_reserve_memory();
-
 #ifdef CONFIG_MEMORY_HOTPLUG
 	/*
 	 * Memory used by the kernel cannot be hot-removed because Linux