[PATCH for-4.14 v2 1/2] x86/passthrough: do not assert edge triggered GSIs for PVH dom0

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Edge triggered interrupts do not assert the line, so the handling done
in Xen should also avoid asserting it. Asserting the line prevents
further edge triggered interrupts on the same vIO-APIC pin from being
delivered, since the line is not de-asserted.

One case of such kind of interrupt is the RTC timer, which is edge
triggered and available to a PVH dom0. Note this should not affect
domUs, as it only modifies the behavior of IDENTITY_GSI kind of passed
through interrupts.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
Changes since v1:
 - Compare the triggering against VIOAPIC_{EDGE/LEVEL}_TRIG.
---
 xen/arch/x86/hvm/irq.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/xen/arch/x86/hvm/irq.c b/xen/arch/x86/hvm/irq.c
index 9c8adbc495..fd02cf2e8d 100644
--- a/xen/arch/x86/hvm/irq.c
+++ b/xen/arch/x86/hvm/irq.c
@@ -169,9 +169,10 @@ void hvm_pci_intx_deassert(
 
 void hvm_gsi_assert(struct domain *d, unsigned int gsi)
 {
+    int trig = vioapic_get_trigger_mode(d, gsi);
     struct hvm_irq *hvm_irq = hvm_domain_irq(d);
 
-    if ( gsi >= hvm_irq->nr_gsis )
+    if ( gsi >= hvm_irq->nr_gsis || trig < 0 )
     {
         ASSERT_UNREACHABLE();
         return;
@@ -186,9 +187,10 @@ void hvm_gsi_assert(struct domain *d, unsigned int gsi)
      * to know if the GSI is pending or not.
      */
     spin_lock(&d->arch.hvm.irq_lock);
-    if ( !hvm_irq->gsi_assert_count[gsi] )
+    if ( trig == VIOAPIC_EDGE_TRIG || !hvm_irq->gsi_assert_count[gsi] )
     {
-        hvm_irq->gsi_assert_count[gsi] = 1;
+        if ( trig == VIOAPIC_LEVEL_TRIG )
+            hvm_irq->gsi_assert_count[gsi] = 1;
         assert_gsi(d, gsi);
     }
     spin_unlock(&d->arch.hvm.irq_lock);
@@ -196,11 +198,12 @@ void hvm_gsi_assert(struct domain *d, unsigned int gsi)
 
 void hvm_gsi_deassert(struct domain *d, unsigned int gsi)
 {
+    int trig = vioapic_get_trigger_mode(d, gsi);
     struct hvm_irq *hvm_irq = hvm_domain_irq(d);
 
-    if ( gsi >= hvm_irq->nr_gsis )
+    if ( trig <= VIOAPIC_EDGE_TRIG || gsi >= hvm_irq->nr_gsis )
     {
-        ASSERT_UNREACHABLE();
+        ASSERT(trig == VIOAPIC_EDGE_TRIG && gsi < hvm_irq->nr_gsis);
         return;
     }
 
-- 
2.26.2