x86/vsmp: Ignore IOAPIC IRQ affinity if possible

vSMP can route interrupts more optimally based on internal
knowledge the OS does not have. In order to support this
optimization, all CPUs must be able to handle all possible
IOAPIC interrupts.

Fix this by setting the vector allocation domain for all CPUs
and by enabling this feature in vSMP.

Signed-off-by: Ravikiran Thirumalai <[e-mail]>
Signed-off-by: Shai Fultheim <[e-mail]>
[ Rebased, simplified, and reworded the commit message. ]
Signed-off-by: Ido Yariv <[e-mail]>
Signed-off-by: Ingo Molnar <[e-mail]>

arch/x86/kernel/vsmp_64.c

···
 #include <linux/pci_ids.h>
 #include <linux/pci_regs.h>
 #include <linux/smp.h>
+#include <linux/irq.h>
 
 #include <asm/apic.h>
 #include <asm/pci-direct.h>
···
 	ctl = readl(address + 4);
 	printk(KERN_INFO "vSMP CTL: capabilities:0x%08x  control:0x%08x\n",
 	       cap, ctl);
+
+	/* If possible, let the vSMP foundation route the interrupt optimally */
+#ifdef CONFIG_SMP
+	if (cap & ctl & BIT(8)) {
+		ctl &= ~BIT(8);
+		no_irq_affinity = 1;
+	}
+#endif
+
 	if (cap & ctl & (1 << 4)) {
 		/* Setup irq ops and turn on vSMP  IRQ fastpath handling */
 		pv_irq_ops.irq_disable = PV_CALLEE_SAVE(vsmp_irq_disable);
···
 		pv_irq_ops.save_fl  = PV_CALLEE_SAVE(vsmp_save_fl);
 		pv_irq_ops.restore_fl  = PV_CALLEE_SAVE(vsmp_restore_fl);
 		pv_init_ops.patch = vsmp_patch;
-
 		ctl &= ~(1 << 4);
-		writel(ctl, address + 4);
-		ctl = readl(address + 4);
-		printk(KERN_INFO "vSMP CTL: control set to:0x%08x\n", ctl);
 	}
+	writel(ctl, address + 4);
+	ctl = readl(address + 4);
+	pr_info("vSMP CTL: control set to:0x%08x\n", ctl);
 
 	early_iounmap(address, 8);
 }
···
 	return hard_smp_processor_id() >> index_msb;
 }
 
+/*
+ * In vSMP, all cpus should be capable of handling interrupts, regardless of
+ * the APIC used.
+ */
+static void fill_vector_allocation_domain(int cpu, struct cpumask *retmask)
+{
+	cpumask_setall(retmask);
+}
+
 static void vsmp_apic_post_init(void)
 {
 	/* need to update phys_pkg_id */
 	apic->phys_pkg_id = apicid_phys_pkg_id;
+	apic->vector_allocation_domain = fill_vector_allocation_domain;
 }
 
 void __init vsmp_init(void)