ACPI/APEI: accept validly sized ERST on Intel systems only for now

Various AMD systems (but [unfortunately] not mine) hang when the table
size check passes. Allow the check to pass on Intel systems only for
now (until someone can actually debug the problem).

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/drivers/acpi/apei/erst.c
+++ b/xen/drivers/acpi/apei/erst.c
@@ -769,6 +769,19 @@ static int __init erst_check_table(struc
 
 	switch (erst_tab->header_length) {
 	case sizeof(*erst_tab) - sizeof(erst_tab->header):
+#ifdef CONFIG_X86
+		/* XXX
+		 * While the rest of the ERST code appears to work on Intel
+		 * systems with properly sized tables, various AMD systems
+		 * appear to get hung (at boot time) by allowing this. Until
+		 * someone with access to suitable hardware can debug this,
+		 * disable the rest of the code by considering this case
+		 * invalid.
+		 */
+		if (boot_cpu_data.x86_vendor != X86_VENDOR_INTEL)
+			return -EINVAL;
+		/* fall through */
+#endif
 	/*
 	 * While invalid per specification, there are (early?) systems
 	 * indicating the full header size here, so accept that value too.