x86: honor ACPI indicating absence of CMOS RTC

On such systems we can boot through EFI only.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Keir Fraser <keir@xen.org>

diff --git a/xen/arch/x86/time.c b/xen/arch/x86/time.c
index 244b43e7f02b6aec997c6787da14f45fca4072bc..56bffdbe3918e885cd95364028e460022ec950e7 100644 (file)
--- a/xen/arch/x86/time.c
+++ b/xen/arch/x86/time.c
@@ -754,6 +754,9 @@ static unsigned long get_cmos_time(void)
             return res;
     }
 
+    if ( unlikely(acpi_gbl_FADT.boot_flags & ACPI_FADT_NO_CMOS_RTC) )
+        panic("System without CMOS RTC must be booted from EFI\n");
+
     spin_lock_irqsave(&rtc_lock, flags);
 
     /* read RTC exactly on falling edge of update flag */