Block out all interrupts, even machine checks, for critical_enter()

This is will be required to prevent lowering the ipl when a critical_enter()
is present in the interrupt path when handling a machine check.

reviewed by: jhb

sys/alpha/include/alpha_cpu.h

@@ -103,6 +103,7 @@ struct alpha_pcb {
 #define	ALPHA_PSL_IPL_IO	0x0004		/* I/O dev ints disabled */
 #define	ALPHA_PSL_IPL_CLOCK	0x0005		/* clock ints disabled */
 #define	ALPHA_PSL_IPL_HIGH	0x0006		/* all but mchecks disabled */
+#define	ALPHA_PSL_IPL_MCES	0x0007		/* all interrupts disabled */
 
 #define	ALPHA_PSL_MUST_BE_ZERO	0xfffffffffffffff0
 

sys/alpha/include/cpufunc.h

@@ -48,7 +48,7 @@ breakpoint(void)
 static __inline critical_t
 critical_enter(void)
 {
-	return (alpha_pal_swpipl(ALPHA_PSL_IPL_HIGH));
+	return (alpha_pal_swpipl(ALPHA_PSL_IPL_MCES));
 }
 
 static __inline void