x86/IRQ: conditionally preserve irq <-> pirq mapping on map error paths

Mappings that had been set up before should not be torn down when
handling unrelated errors.

This is part of XSA-237.

Reported-by: HW42 <hw42@ipsumj.de>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Reviewed-by: George Dunlap <george.dunlap@citrix.com>

xen/arch/x86/irq.c

@@ -1259,7 +1259,8 @@ static int prepare_domain_irq_pirq(struct domain *d, int irq, int pirq,
         return -ENOMEM;
     }
     *pinfo = info;
-    return 0;
+
+    return !!err;
 }
 
 static void set_domain_irq_pirq(struct domain *d, int irq, struct pirq *pirq)
@@ -1302,7 +1303,10 @@ int init_domain_irq_mapping(struct domain *d)
             continue;
         err = prepare_domain_irq_pirq(d, i, i, &info);
         if ( err )
+        {
+            ASSERT(err < 0);
             break;
+        }
         set_domain_irq_pirq(d, i, info);
     }
 
@@ -1903,6 +1907,8 @@ int get_free_pirqs(struct domain *d, unsigned int nr)
     return -ENOSPC;
 }
 
+#define MAX_MSI_IRQS 32 /* limited by MSI capability struct properties */
+
 int map_domain_pirq(
     struct domain *d, int pirq, int irq, int type, void *data)
 {
@@ -1911,6 +1917,7 @@ int map_domain_pirq(
     struct pirq *info;
     struct irq_desc *desc;
     unsigned long flags;
+    DECLARE_BITMAP(prepared, MAX_MSI_IRQS) = {};
 
     ASSERT(spin_is_locked(&d->event_lock));
 
@@ -1954,8 +1961,10 @@ int map_domain_pirq(
     }
 
     ret = prepare_domain_irq_pirq(d, irq, pirq, &info);
-    if ( ret )
+    if ( ret < 0 )
         goto revoke;
+    if ( !ret )
+        __set_bit(0, prepared);
 
     desc = irq_to_desc(irq);
 
@@ -2027,8 +2036,10 @@ int map_domain_pirq(
             irq = create_irq(NUMA_NO_NODE);
             ret = irq >= 0 ? prepare_domain_irq_pirq(d, irq, pirq + nr, &info)
                            : irq;
-            if ( ret )
+            if ( ret < 0 )
                 break;
+            if ( !ret )
+                __set_bit(nr, prepared);
             msi_desc[nr].irq = irq;
 
             if ( irq_permit_access(d, irq) != 0 )
@@ -2061,15 +2072,15 @@ int map_domain_pirq(
                 desc->msi_desc = NULL;
                 spin_unlock_irqrestore(&desc->lock, flags);
             }
-            while ( nr-- )
+            while ( nr )
             {
                 if ( irq >= 0 && irq_deny_access(d, irq) )
                     printk(XENLOG_G_ERR
                            "dom%d: could not revoke access to IRQ%d (pirq %d)\n",
                            d->domain_id, irq, pirq);
-                if ( info )
+                if ( info && test_bit(nr, prepared) )
                     cleanup_domain_irq_pirq(d, irq, info);
-                info = pirq_info(d, pirq + nr);
+                info = pirq_info(d, pirq + --nr);
                 irq = info->arch.irq;
             }
             msi_desc->irq = -1;
@@ -2085,12 +2096,14 @@ int map_domain_pirq(
         spin_lock_irqsave(&desc->lock, flags);
         set_domain_irq_pirq(d, irq, info);
         spin_unlock_irqrestore(&desc->lock, flags);
+        ret = 0;
     }
 
 done:
     if ( ret )
     {
-        cleanup_domain_irq_pirq(d, irq, info);
+        if ( test_bit(0, prepared) )
+            cleanup_domain_irq_pirq(d, irq, info);
  revoke:
         if ( irq_deny_access(d, irq) )
             printk(XENLOG_G_ERR
@@ -2565,7 +2578,7 @@ static int allocate_pirq(struct domain *d, int index, int pirq, int irq,
         }
         else if ( type == MAP_PIRQ_TYPE_MULTI_MSI )
         {
-            if ( *nr <= 0 || *nr > 32 )
+            if ( *nr <= 0 || *nr > MAX_MSI_IRQS )
                 return -EDOM;
             if ( *nr != 1 && !iommu_intremap )
                 return -EOPNOTSUPP;