x86: consistently serialize CMOS/RTC accesses on rtc_lock

Since RTC/CMOS accesses aren't atomic, there are possible races
between code paths setting the index register and subsequently
reading/writing the data register. This is supposed to be dealt with
by acquiring rtc_lock, but two places up to now lacked respective
synchronization: Accesses to the EFI time functions and
smpboot_{setup,restore}_warm_reset_vector().

This in turn requires no longer directly passing through guest writes
to the index register, but instead using a machanism similar to that
for PCI config space method 1 accesses.

Signed-off-by: Jan Beulich <jbeulich@novell.com>

1 files changed, 2 insertions, 10 deletions

diff --git a/xen/arch/x86/hpet.c b/xen/arch/x86/hpet.c
index 2f8c957d75..f3a298fefc 100644
--- a/xen/arch/x86/hpet.c
+++ b/xen/arch/x86/hpet.c
@@ -502,18 +502,10 @@ static void hpet_detach_channel(unsigned int cpu,
 
 #include <asm/mc146818rtc.h>
 
-void (*__read_mostly pv_rtc_handler)(unsigned int port, uint8_t value);
+void (*__read_mostly pv_rtc_handler)(uint8_t index, uint8_t value);
 
-static void handle_rtc_once(unsigned int port, uint8_t value)
+static void handle_rtc_once(uint8_t index, uint8_t value)
 {
-    static int index;
-
-    if ( port == 0x70 )
-    {
-        index = value;
-        return;
-    }
-
     if ( index != RTC_REG_B )
         return;