x86: Use u32 instead of long to set reset vector back to 0

A customer of ours, complained that when setting the reset
vector back to 0, it trashed other data and hung their box.
They noticed when only 4 bytes were set to 0 instead of 8,
everything worked correctly.

Mathew pointed out:

 |
 | We're supposed to be resetting trampoline_phys_low and
 | trampoline_phys_high here, which are two 16-bit values.
 | Writing 64 bits is definitely going to overwrite space
 | that we're not supposed to be touching.
 |

So limit the area modified to u32.

Signed-off-by: Don Zickus <[email protected]>
Acked-by: Matthew Garrett <[email protected]>
Cc: <[email protected]>
LKML-Reference: <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>

arch/x86/include/asm/smpboot_hooks.h

@@ -34,7 +34,7 @@ static inline void smpboot_restore_warm_reset_vector(void)
 	 */
 	CMOS_WRITE(0, 0xf);
 
-	*((volatile long *)phys_to_virt(apic->trampoline_phys_low)) = 0;
+	*((volatile u32 *)phys_to_virt(apic->trampoline_phys_low)) = 0;
 }
 
 static inline void __init smpboot_setup_io_apic(void)