x86/passthrough: introduce a flag for GSIs not requiring an EOI or unmask

There's no need to setup a timer for GSIs that are edge triggered,
since those don't require any EIO or unmask, and hence couldn't block
other interrupts.

Note this is only used by PVH dom0, that can setup the passthrough of
edge triggered interrupts from the vIO-APIC. One example of such kind
of interrupt that can be used by a PVH dom0 would be the RTC timer.

While there introduce an out label to do the unlock and reduce code
duplication.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Paul Durrant <paul@xen.org>

xen/drivers/passthrough/io.c

@@ -138,7 +138,8 @@ static void pt_pirq_softirq_reset(struct hvm_pirq_dpci *pirq_dpci)
 
 bool pt_irq_need_timer(uint32_t flags)
 {
-    return !(flags & (HVM_IRQ_DPCI_GUEST_MSI | HVM_IRQ_DPCI_TRANSLATE));
+    return !(flags & (HVM_IRQ_DPCI_GUEST_MSI | HVM_IRQ_DPCI_TRANSLATE |
+                      HVM_IRQ_DPCI_NO_EOI));
 }
 
 static int pt_irq_guest_eoi(struct domain *d, struct hvm_pirq_dpci *pirq_dpci,
@@ -558,6 +559,12 @@ int pt_irq_create_bind(
                      */
                     ASSERT(!mask);
                     share = trigger_mode;
+                    if ( trigger_mode == VIOAPIC_EDGE_TRIG )
+                        /*
+                         * Edge IO-APIC interrupt, no EOI or unmask to perform
+                         * and hence no timer needed.
+                         */
+                        pirq_dpci->flags |= HVM_IRQ_DPCI_NO_EOI;
                 }
             }
 
@@ -897,17 +904,13 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
             send_guest_pirq(d, pirq);
 
             if ( pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI )
-            {
-                spin_unlock(&d->event_lock);
-                return;
-            }
+                goto out;
         }
 
         if ( pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI )
         {
             vmsi_deliver_pirq(d, pirq_dpci);
-            spin_unlock(&d->event_lock);
-            return;
+            goto out;
         }
 
         list_for_each_entry ( digl, &pirq_dpci->digl_list, list )
@@ -920,6 +923,8 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
         if ( pirq_dpci->flags & HVM_IRQ_DPCI_IDENTITY_GSI )
         {
             hvm_gsi_assert(d, pirq->pirq);
+            if ( pirq_dpci->flags & HVM_IRQ_DPCI_NO_EOI )
+                goto out;
             pirq_dpci->pending++;
         }
 
@@ -927,8 +932,7 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
         {
             /* for translated MSI to INTx interrupt, eoi as early as possible */
             __msi_pirq_eoi(pirq_dpci);
-            spin_unlock(&d->event_lock);
-            return;
+            goto out;
         }
 
         /*
@@ -941,6 +945,8 @@ static void hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci)
         ASSERT(pt_irq_need_timer(pirq_dpci->flags));
         set_timer(&pirq_dpci->timer, NOW() + PT_IRQ_TIME_OUT);
     }
+
+ out:
     spin_unlock(&d->event_lock);
 }
 

xen/include/asm-x86/hvm/irq.h

@@ -121,6 +121,7 @@ struct dev_intx_gsi_link {
 #define _HVM_IRQ_DPCI_GUEST_PCI_SHIFT           4
 #define _HVM_IRQ_DPCI_GUEST_MSI_SHIFT           5
 #define _HVM_IRQ_DPCI_IDENTITY_GSI_SHIFT        6
+#define _HVM_IRQ_DPCI_NO_EOI_SHIFT              7
 #define _HVM_IRQ_DPCI_TRANSLATE_SHIFT          15
 #define HVM_IRQ_DPCI_MACH_PCI        (1u << _HVM_IRQ_DPCI_MACH_PCI_SHIFT)
 #define HVM_IRQ_DPCI_MACH_MSI        (1u << _HVM_IRQ_DPCI_MACH_MSI_SHIFT)
@@ -129,6 +130,7 @@ struct dev_intx_gsi_link {
 #define HVM_IRQ_DPCI_GUEST_PCI       (1u << _HVM_IRQ_DPCI_GUEST_PCI_SHIFT)
 #define HVM_IRQ_DPCI_GUEST_MSI       (1u << _HVM_IRQ_DPCI_GUEST_MSI_SHIFT)
 #define HVM_IRQ_DPCI_IDENTITY_GSI    (1u << _HVM_IRQ_DPCI_IDENTITY_GSI_SHIFT)
+#define HVM_IRQ_DPCI_NO_EOI          (1u << _HVM_IRQ_DPCI_NO_EOI_SHIFT)
 #define HVM_IRQ_DPCI_TRANSLATE       (1u << _HVM_IRQ_DPCI_TRANSLATE_SHIFT)
 
 struct hvm_gmsi_info {