diff --git a/arch/i386/kernel/io_apic.c b/arch/i386/kernel/io_apic.c
index 350192d..507983c 100644
--- a/arch/i386/kernel/io_apic.c
+++ b/arch/i386/kernel/io_apic.c
@@ -91,6 +91,46 @@
 	int apic, pin, next;
 } irq_2_pin[PIN_MAP_SIZE];
 
+struct io_apic {
+	unsigned int index;
+	unsigned int unused[3];
+	unsigned int data;
+};
+
+static __attribute_const__ struct io_apic __iomem *io_apic_base(int idx)
+{
+	return (void __iomem *) __fix_to_virt(FIX_IO_APIC_BASE_0 + idx)
+		+ (mp_ioapics[idx].mpc_apicaddr & ~PAGE_MASK);
+}
+
+static inline unsigned int io_apic_read(unsigned int apic, unsigned int reg)
+{
+	struct io_apic __iomem *io_apic = io_apic_base(apic);
+	writel(reg, &io_apic->index);
+	return readl(&io_apic->data);
+}
+
+static inline void io_apic_write(unsigned int apic, unsigned int reg, unsigned int value)
+{
+	struct io_apic __iomem *io_apic = io_apic_base(apic);
+	writel(reg, &io_apic->index);
+	writel(value, &io_apic->data);
+}
+
+/*
+ * Re-write a value: to be used for read-modify-write
+ * cycles where the read already set up the index register.
+ *
+ * Older SiS APIC requires we rewrite the index register
+ */
+static inline void io_apic_modify(unsigned int apic, unsigned int reg, unsigned int value)
+{
+	volatile struct io_apic *io_apic = io_apic_base(apic);
+	if (sis_apic_bug)
+		writel(reg, &io_apic->index);
+	writel(value, &io_apic->data);
+}
+
 union entry_union {
 	struct { u32 w1, w2; };
 	struct IO_APIC_route_entry entry;
@@ -107,12 +147,34 @@
 	return eu.entry;
 }
 
+/*
+ * When we write a new IO APIC routing entry, we need to write the high
+ * word first! If the mask bit in the low word is clear, we will enable
+ * the interrupt, and we need to make sure the entry is fully populated
+ * before that happens.
+ */
 static void ioapic_write_entry(int apic, int pin, struct IO_APIC_route_entry e)
 {
 	unsigned long flags;
 	union entry_union eu;
 	eu.entry = e;
 	spin_lock_irqsave(&ioapic_lock, flags);
+	io_apic_write(apic, 0x11 + 2*pin, eu.w2);
+	io_apic_write(apic, 0x10 + 2*pin, eu.w1);
+	spin_unlock_irqrestore(&ioapic_lock, flags);
+}
+
+/*
+ * When we mask an IO APIC routing entry, we need to write the low
+ * word first, in order to set the mask bit before we change the
+ * high bits!
+ */
+static void ioapic_mask_entry(int apic, int pin)
+{
+	unsigned long flags;
+	union entry_union eu = { .entry.mask = 1 };
+
+	spin_lock_irqsave(&ioapic_lock, flags);
 	io_apic_write(apic, 0x10 + 2*pin, eu.w1);
 	io_apic_write(apic, 0x11 + 2*pin, eu.w2);
 	spin_unlock_irqrestore(&ioapic_lock, flags);
@@ -234,9 +296,7 @@
 	/*
 	 * Disable it in the IO-APIC irq-routing table:
 	 */
-	memset(&entry, 0, sizeof(entry));
-	entry.mask = 1;
-	ioapic_write_entry(apic, pin, entry);
+	ioapic_mask_entry(apic, pin);
 }
 
 static void clear_IO_APIC (void)
diff --git a/include/asm-i386/io_apic.h b/include/asm-i386/io_apic.h
index 276ea7e..059a9ff 100644
--- a/include/asm-i386/io_apic.h
+++ b/include/asm-i386/io_apic.h
@@ -12,10 +12,6 @@
 
 #ifdef CONFIG_X86_IO_APIC
 
-#define IO_APIC_BASE(idx) \
-		((volatile int *)(__fix_to_virt(FIX_IO_APIC_BASE_0 + idx) \
-		+ (mp_ioapics[idx].mpc_apicaddr & ~PAGE_MASK)))
-
 /*
  * The structure of the IO-APIC:
  */
@@ -119,31 +115,8 @@
 /* non-0 if default (table-less) MP configuration */
 extern int mpc_default_type;
 
-static inline unsigned int io_apic_read(unsigned int apic, unsigned int reg)
-{
-	*IO_APIC_BASE(apic) = reg;
-	return *(IO_APIC_BASE(apic)+4);
-}
-
-static inline void io_apic_write(unsigned int apic, unsigned int reg, unsigned int value)
-{
-	*IO_APIC_BASE(apic) = reg;
-	*(IO_APIC_BASE(apic)+4) = value;
-}
-
-/*
- * Re-write a value: to be used for read-modify-write
- * cycles where the read already set up the index register.
- *
- * Older SiS APIC requires we rewrite the index regiser
- */
+/* Older SiS APIC requires we rewrite the index register */
 extern int sis_apic_bug;
-static inline void io_apic_modify(unsigned int apic, unsigned int reg, unsigned int value)
-{
-	if (sis_apic_bug)
-		*IO_APIC_BASE(apic) = reg;
-	*(IO_APIC_BASE(apic)+4) = value;
-}
 
 /* 1 if "noapic" boot option passed */
 extern int skip_ioapic_setup;