x86/ioapic: Fix signed shifts in io_apic.c

There exists bitshifts in the IOAPIC code where signed integers are
shifted to the left by up to 31 bits, which is undefined behaviour.

This patch fixes this by changing the integers from signed to unsigned.

Signed-off-by: Matthew Barnes <[email protected]>
Reviewed-by: Jan Beulich <[email protected]>
Reviewed-by: Andrew Cooper <[email protected]>
Release-Acked-By: Oleksii Kurochko <[email protected]>

xen/arch/x86/io_apic.c

@@ -1692,7 +1692,8 @@ static void cf_check mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
        !io_apic_level_ack_pending(desc->irq))
         move_masked_irq(desc);
 
-    if ( !(v & (1 << (i & 0x1f))) ) {
+    if ( !(v & (1U << (i & 0x1f))) )
+    {
         spin_lock(&ioapic_lock);
         __edge_IO_APIC_irq(desc->irq);
         __level_IO_APIC_irq(desc->irq);
@@ -1756,7 +1757,8 @@ static void cf_check end_level_ioapic_irq_new(struct irq_desc *desc, u8 vector)
          !io_apic_level_ack_pending(desc->irq) )
         move_native_irq(desc);
 
-    if (!(v & (1 << (i & 0x1f)))) {
+    if ( !(v & (1U << (i & 0x1f))) )
+    {
         spin_lock(&ioapic_lock);
         __mask_IO_APIC_irq(desc->irq);
         __edge_IO_APIC_irq(desc->irq);