[PATCH v2 1/5] x86/pass-through: alter locking around pt_irq_{create,destroy}_bind()

[Jan Beulich <jbeulich@xxxxxxxx>]

The questionable use of pcidevs_lock() there was discussed more than once.
It really is pointless: The functions synchronize primarily via the per-
domain event lock. They also may already be called with the global PCI
devices lock not held: See hvm/vmsi.c:vpci_msi_update(),
hvm/vmsi.c:vpci_msi_arch_update(), and hvm/vmsi.c:vpci_msi_disable().

It's merely msixtbl_pt_{,un}register() which require the global or per-
domain PCI lock held. Switch to using the latter, which is also sufficient
to acquire in read mode. While strictly speaking this is needed only for
PT_IRQ_TYPE_MSI, keep it being unconditional. In vioapic_hwdom_map_gsi()
also unlock earlier.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v2: Replace locking rather than dropping it altogether.

--- a/xen/arch/x86/domctl.c
+++ b/xen/arch/x86/domctl.c
@@ -636,9 +636,9 @@ long arch_do_domctl(
             ret = -EPERM;
         else if ( is_iommu_enabled(d) )
         {
-            pcidevs_lock();
+            read_lock(&d->pci_lock);
             ret = pt_irq_create_bind(d, bind);
-            pcidevs_unlock();
+            read_unlock(&d->pci_lock);
 
             if ( ret < 0 )
                 printk(XENLOG_G_ERR "pt_irq_create_bind failed (%ld) for 
%pd\n",
@@ -670,9 +670,9 @@ long arch_do_domctl(
             ret = -EPERM;
         else if ( is_iommu_enabled(d) )
         {
-            pcidevs_lock();
+            read_lock(&d->pci_lock);
             ret = pt_irq_destroy_bind(d, bind);
-            pcidevs_unlock();
+            read_unlock(&d->pci_lock);
 
             if ( ret < 0 )
                 printk(XENLOG_G_ERR "pt_irq_destroy_bind failed (%ld) for 
%pd\n",
--- a/xen/arch/x86/hvm/vioapic.c
+++ b/xen/arch/x86/hvm/vioapic.c
@@ -197,8 +197,9 @@ static int vioapic_hwdom_map_gsi(unsigne
         return ret;
     }
 
-    pcidevs_lock();
+    read_lock(&currd->pci_lock);
     ret = pt_irq_create_bind(currd, &pt_irq_bind);
+    read_unlock(&currd->pci_lock);
     if ( ret )
     {
         gprintk(XENLOG_WARNING, "vioapic: error binding GSI %u: %d\n",
@@ -207,7 +208,6 @@ static int vioapic_hwdom_map_gsi(unsigne
         unmap_domain_pirq(currd, pirq);
         write_unlock(&currd->event_lock);
     }
-    pcidevs_unlock();
 
     return ret;
 }