bitkeeper revision 1.1159.213.2 (41dc5bb8NoFeyC8xMcZdstILsQ-Tqg)

patch from Leendert van Doorn <leendert@watson.ibm.com>

Hyperthreading on VMX is broken in the xeno-unstable.bk tree. The diff
below fixes this.
It turns out that the mtrr code clears too many bits, some of them cause
Xen to crash. Being a bit more precise fixes the problem.

xen/arch/x86/mtrr/generic.c

@@ -250,7 +250,7 @@ static void prepare_set(void)
 	/*  Save value of CR4 and clear Page Global Enable (bit 7)  */
 	if ( cpu_has_pge ) {
 		cr4 = read_cr4();
-		write_cr4(cr4 & (unsigned char) ~(1 << 7));
+		write_cr4(cr4 & ~X86_CR4_PGE);
 	}
 
 	/* Flush all TLBs via a mov %cr3, %reg; mov %reg, %cr3 */