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, 8 insertions, 0 deletions

diff --git a/xen/include/asm-x86/mach-default/smpboot_hooks.h b/xen/include/asm-x86/mach-default/smpboot_hooks.h
index a70d279912..14e1ee52a3 100644
--- a/xen/include/asm-x86/mach-default/smpboot_hooks.h
+++ b/xen/include/asm-x86/mach-default/smpboot_hooks.h
@@ -3,7 +3,11 @@
 
 static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 {
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc_lock, flags);
 	CMOS_WRITE(0xa, 0xf);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 	flush_tlb_local();
 	Dprintk("1.\n");
 	*((volatile unsigned short *) TRAMPOLINE_HIGH) = start_eip >> 4;
@@ -14,6 +18,8 @@ static inline void smpboot_setup_warm_reset_vector(unsigned long start_eip)
 
 static inline void smpboot_restore_warm_reset_vector(void)
 {
+	unsigned long flags;
+
 	/*
 	 * Install writable page 0 entry to set BIOS data area.
 	 */
@@ -23,7 +29,9 @@ static inline void smpboot_restore_warm_reset_vector(void)
 	 * Paranoid:  Set warm reset code and vector here back
 	 * to default values.
 	 */
+	spin_lock_irqsave(&rtc_lock, flags);
 	CMOS_WRITE(0, 0xf);
+	spin_unlock_irqrestore(&rtc_lock, flags);
 
 	*((volatile int *) maddr_to_virt(0x467)) = 0;
 }