x86/ioapic: Add register level checks to detect bogus io-apic entries

With the recent changes to clear_IO_APIC_pin() which tries to
clear remoteIRR bit explicitly, some of the users started to see
"Unable to reset IRR for apic .." messages.

Close look shows that these are related to bogus IO-APIC entries
which returns all 1s for their io-apic registers. And the
above mentioned error messages are benign. But kernel should
have ignored such io-apic's in the first place.

Check if register 0, 1, 2 of the listed io-apic are all 1s and
ignore such io-apic.

[original Linux patch:]
Signed-off-by: Suresh Siddha <suresh.b.siddha@xxxxxxxxx>
Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -185,7 +185,7 @@ struct IO_APIC_route_entry **alloc_ioapi
         ioapic_entries[apic] =
             xmalloc_array(struct IO_APIC_route_entry,
                           nr_ioapic_entries[apic]);
-        if (!ioapic_entries[apic])
+        if (!ioapic_entries[apic] && nr_ioapic_entries[apic])
             goto nomem;
     }
 
@@ -310,6 +310,9 @@ int save_IO_APIC_setup(struct IO_APIC_ro
         return -ENOMEM;
 
     for (apic = 0; apic < nr_ioapics; apic++) {
+        if (!nr_ioapic_entries[apic])
+            continue;
+
         if (!ioapic_entries[apic])
             return -ENOMEM;
 
@@ -331,6 +334,9 @@ void mask_IO_APIC_setup(struct IO_APIC_r
         return;
 
     for (apic = 0; apic < nr_ioapics; apic++) {
+        if (!nr_ioapic_entries[apic])
+            continue;
+
         if (!ioapic_entries[apic])
             break;
 
@@ -358,6 +364,9 @@ int restore_IO_APIC_setup(struct IO_APIC
         return -ENOMEM;
 
     for (apic = 0; apic < nr_ioapics; apic++) {
+        if (!nr_ioapic_entries[apic])
+            continue;
+
         if (!ioapic_entries[apic])
             return -ENOMEM;
 
@@ -610,6 +619,8 @@ static int __init find_isa_irq_apic(int 
     if (i < mp_irq_entries) {
         int apic;
         for(apic = 0; apic < nr_ioapics; apic++) {
+            if (!nr_ioapic_entries[apic])
+                continue;
             if (mp_ioapics[apic].mpc_apicid == mp_irqs[i].mpc_dstapic)
                 return apic;
         }
@@ -1080,6 +1091,8 @@ static void /*__init*/ __print_IO_APIC(v
     printk(KERN_INFO "testing the IO APIC.......................\n");
 
     for (apic = 0; apic < nr_ioapics; apic++) {
+        if (!nr_ioapic_entries[apic])
+            continue;
 
 	spin_lock_irqsave(&ioapic_lock, flags);
 	reg_00.raw = io_apic_read(apic, 0);
@@ -1229,6 +1242,8 @@ static void __init enable_IO_APIC(void)
 
     if (directed_eoi_enabled) {
         for (apic = 0; apic < nr_ioapics; apic++) {
+            if (!nr_ioapic_entries[apic])
+                continue;
             vector_map[apic] = xzalloc(vmask_t);
             BUG_ON(!vector_map[apic]);
         }
@@ -1354,6 +1369,8 @@ static void __init setup_ioapic_ids_from
      * Set the IOAPIC ID to the value stored in the MPC table.
      */
     for (apic = 0; apic < nr_ioapics; apic++) {
+        if (!nr_ioapic_entries[apic])
+            continue;
 
         /* Read the register 0 value */
         spin_lock_irqsave(&ioapic_lock, flags);
@@ -2038,6 +2055,8 @@ void ioapic_resume(void)
 
     spin_lock_irqsave(&ioapic_lock, flags);
     for (apic = 0; apic < nr_ioapics; apic++){
+        if (!nr_ioapic_entries[apic])
+            continue;
         reg_00.raw = __io_apic_read(apic, 0);
         if (reg_00.bits.ID != mp_ioapics[apic].mpc_apicid) {
             reg_00.bits.ID = mp_ioapics[apic].mpc_apicid;
@@ -2225,8 +2244,12 @@ static int ioapic_physbase_to_id(unsigne
 {
     int apic;
     for ( apic = 0; apic < nr_ioapics; apic++ )
+    {
+        if ( !nr_ioapic_entries[apic] )
+            continue;
         if ( mp_ioapics[apic].mpc_apicaddr == physbase )
             return apic;
+    }
     return -EINVAL;
 }
 
@@ -2444,6 +2467,22 @@ void dump_ioapic_irq_info(void)
 static unsigned int __initdata max_gsi_irqs;
 integer_param("max_gsi_irqs", max_gsi_irqs);
 
+static __init bool_t bad_ioapic_register(unsigned int idx)
+{
+    union IO_APIC_reg_00 reg_00 = { .raw = io_apic_read(idx, 0) };
+    union IO_APIC_reg_01 reg_01 = { .raw = io_apic_read(idx, 1) };
+    union IO_APIC_reg_02 reg_02 = { .raw = io_apic_read(idx, 2) };
+
+    if ( reg_00.raw == -1 && reg_01.raw == -1 && reg_02.raw == -1 )
+    {
+        printk(KERN_WARNING "I/O APIC %#x registers return all ones, skipping!\n",
+               mp_ioapics[idx].mpc_apicaddr);
+        return 1;
+    }
+
+    return 0;
+}
+
 void __init init_ioapic_mappings(void)
 {
     unsigned long ioapic_phys;
@@ -2477,6 +2516,12 @@ void __init init_ioapic_mappings(void)
                     __fix_to_virt(idx), ioapic_phys);
         idx++;
 
+        if ( bad_ioapic_register(i) )
+        {
+            __set_fixmap(idx, 0, 0);
+            continue;
+        }
+
         if ( smp_found_config )
         {
             /* The number of IO-APIC IRQ registers (== #pins): */