[PATCH] Fix memory corruption at x86-64 SMP bootup

This fixes a long standing corruption bug in the x86-64 code. The SMP
trampoline would corrupt page 2, which was sometimes used for other
data.  This corrupted the ioport/iomem list in some cases and causes
oopses while read /proc/iomem.

Fix is to check the correct location and don't zero it afterwards
because it gets reinitialized for the next CPU anyways.

Thanks to Alexander Nyberg for tracking it down.

arch/x86_64/kernel/smpboot.c

@@ -659,7 +659,7 @@ static void __init do_boot_cpu (int apicid)
 			Dprintk("CPU has booted.\n");
 		} else {
 			boot_error = 1;
-			if (*((volatile unsigned char *)phys_to_virt(8192))
+			if (*((volatile unsigned char *)phys_to_virt(SMP_TRAMPOLINE_BASE))
 					== 0xA5)
 				/* trampoline started but...? */
 				printk("Stuck ??\n");
@@ -676,9 +676,6 @@ static void __init do_boot_cpu (int apicid)
 		clear_bit(cpu, &cpu_initialized); /* was set by cpu_init() */
 		cpucount--;
 	}
-
-	/* mark "stuck" area as not stuck */
-	*((volatile unsigned *)phys_to_virt(8192)) = 0;
 }
 
 cycles_t cacheflush_time;