Comment 3 for bug 854829

Stefano Stabellini replied:

Thanks for the very detailed analysis. It seems to me that the problem is that if the interrupt is a level
triggered interrupt when the guest issues an EOI we should be reinjecting the interrupt again if it has been issued a second time in the meantime. However this doesn't happen if the interrupt has been remapped onto an even channel. In that case the guest is not even going to issue an EOI at all.
So I wrote a patch to force the guest to issue EOIs even on remapped irqs; in the hypercall handler we check whether we need to reinject the interrupt and if that is the case we set the corresponding event channel pending.
Could you please try the patch I appended? I haven't been able to reproduce your problem so I am not really sure if it works.

diff -r e042fb60e0ee xen/arch/x86/physdev.c
--- a/xen/arch/x86/physdev.c Thu Sep 29 11:23:01 2011 +0000
+++ b/xen/arch/x86/physdev.c Fri Sep 30 14:01:46 2011 +0000
@@ -11,6 +11,7 @@
 #include <asm/current.h>
 #include <asm/io_apic.h>
 #include <asm/msi.h>
+#include <asm/hvm/irq.h>
 #include <asm/hypercall.h>
 #include <public/xen.h>
 #include <public/physdev.h>
@@ -270,6 +271,18 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_H
         if ( !is_hvm_domain(v->domain) ||
              domain_pirq_to_irq(v->domain, eoi.irq) > 0 )
             pirq_guest_eoi(pirq);
+ if ( is_hvm_domain(v->domain) &&
+ domain_pirq_to_emuirq(v->domain, eoi.irq) > 0 )
+ {
+ struct hvm_irq *hvm_irq = &v->domain->arch.hvm_domain.irq;
+ int gsi = domain_pirq_to_emuirq(v->domain, eoi.irq);
+
+ /* if this is a level irq and count > 0, send another
+ * notification */
+ if ( gsi >= NR_ISAIRQS /* ISA irqs are edge triggered */
+ && hvm_irq->gsi_assert_count[gsi] )
+ send_guest_pirq(v->domain, pirq);
+ }
         spin_unlock(&v->domain->event_lock);
         ret = 0;
         break;
@@ -327,12 +340,6 @@ ret_t do_physdev_op(int cmd, XEN_GUEST_H
         if ( (irq < 0) || (irq >= v->domain->nr_pirqs) )
             break;
         irq_status_query.flags = 0;
- if ( is_hvm_domain(v->domain) &&
- domain_pirq_to_irq(v->domain, irq) <= 0 )
- {
- ret = copy_to_guest(arg, &irq_status_query, 1) ? -EFAULT : 0;
- break;
- }

         /*
          * Even edge-triggered or message-based IRQs can need masking from