Re: NetBSD dom0 PVH: hardware interrupts stalls

["Roger Pau Monné" <roger.pau@citrix.com>]

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On Fri, Nov 27, 2020 at 10:44:20PM +0100, Manuel Bouyer wrote:
> On Fri, Nov 27, 2020 at 09:22:11PM +0100, Roger Pau Monné wrote:
> > > 
> > > But I can confirm that now, entering ^A^A^A gets interrupt going in again
> > 
> > I think there are some weird things with dpci interrupts that I'm
> > trying to understand. I have a patch now that will panic when the
> > buffer is full, so we will hopefully be able to see the whole trace of
> > events. There will be no need for you to press the 'T' key now, the
> > system will panic when the buffer is full.
> > 
> > Note this patch also removes the deassert done in pt_irq_time_out.
> 
> thanks
> the trace is at
> http://www-soc.lip6.fr/~bouyer/xen-log13.txt

Thanks! I think I've found the issue and I'm attaching a possible fix
(fix.patch) to this email. In any case I've also attached a further
debug patch, in case the fix turns out to be wrong. Please test the
fix first, as the debug patch will end up triggering a panic when the
buffer is full.

Roger.

[-- Attachment #2: fix.patch --]
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From 232112a292c3b82b3063ea6c7aab56afc8e03f67 Mon Sep 17 00:00:00 2001
From: Roger Pau Monne <roger.pau@citrix.com>
Date: Sat, 28 Nov 2020 15:06:26 +0100
Subject: [PATCH] x86/vioapic: fix usage of index in place of GSI in
 vioapic_write_redirent
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The usage of idx instead of the GSI in vioapic_write_redirent when
accessing gsi_assert_count can cause a PVH dom0 with multiple
vIO-APICs to lose interrupts in case a pin of a IO-APIC different than
the first one is unmasked with pending interrupts.

Switch to use gsi instead to fix the issue.

Fixes: 9f44b08f7d0e4 ('x86/vioapic: introduce support for multiple vIO APICS')
Signed-off-by: Roger Pau Monné <roge.rpau@citrix.com>
---
 xen/arch/x86/hvm/vioapic.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/vioapic.c b/xen/arch/x86/hvm/vioapic.c
index 67d4a6237f..e64abee7a9 100644
--- a/xen/arch/x86/hvm/vioapic.c
+++ b/xen/arch/x86/hvm/vioapic.c
@@ -260,7 +260,7 @@ static void vioapic_write_redirent(
         pent->fields.remote_irr = 0;
     else if ( !ent.fields.mask &&
               !ent.fields.remote_irr &&
-              hvm_irq->gsi_assert_count[idx] )
+              hvm_irq->gsi_assert_count[gsi] )
     {
         pent->fields.remote_irr = 1;
         vioapic_deliver(vioapic, idx);
-- 
2.29.2


[-- Attachment #3: debug.patch --]
[-- Type: text/plain, Size: 7609 bytes --]

diff --git a/xen/arch/x86/hvm/irq.c b/xen/arch/x86/hvm/irq.c
index 38ac5fb6c7..9db3dcc957 100644
--- a/xen/arch/x86/hvm/irq.c
+++ b/xen/arch/x86/hvm/irq.c
@@ -187,6 +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 ( gsi == TRACK_IRQ )
+        debugtrace_printk("hvm_gsi_assert irq %u trig %u assert count %u\n",
+                          gsi, trig, hvm_irq->gsi_assert_count[gsi]);
+
     if ( trig == VIOAPIC_EDGE_TRIG || !hvm_irq->gsi_assert_count[gsi] )
     {
         if ( trig == VIOAPIC_LEVEL_TRIG )
diff --git a/xen/arch/x86/hvm/vioapic.c b/xen/arch/x86/hvm/vioapic.c
index e64abee7a9..df82147f9b 100644
--- a/xen/arch/x86/hvm/vioapic.c
+++ b/xen/arch/x86/hvm/vioapic.c
@@ -257,7 +257,11 @@ static void vioapic_write_redirent(
         vlapic_adjust_i8259_target(d);
     }
     else if ( ent.fields.trig_mode == VIOAPIC_EDGE_TRIG )
+    {
+        if ( gsi == TRACK_IRQ )
+            debugtrace_printk("vIO-APIC set edge trigger irq %u\n", gsi);
         pent->fields.remote_irr = 0;
+    }
     else if ( !ent.fields.mask &&
               !ent.fields.remote_irr &&
               hvm_irq->gsi_assert_count[gsi] )
@@ -278,6 +282,12 @@ static void vioapic_write_redirent(
          */
         int ret = vioapic_hwdom_map_gsi(gsi, ent.fields.trig_mode,
                                         ent.fields.polarity);
+
+        if ( gsi == TRACK_IRQ )
+            debugtrace_printk("vIO-APIC UNMASK irq %u irr %u mask %u assert count %u\n",
+                              gsi, pent->fields.remote_irr, pent->fields.mask,
+                              hvm_irq->gsi_assert_count[gsi]);
+
         if ( ret )
         {
             gprintk(XENLOG_ERR,
@@ -285,6 +295,9 @@ static void vioapic_write_redirent(
             unmasked = 0;
         }
     }
+    else if ( is_hardware_domain(d) && gsi == TRACK_IRQ )
+        debugtrace_printk("vIO-APIC MASK irq %u\n", gsi);
+
 
     if ( gsi == 0 || unmasked )
         pt_may_unmask_irq(d, NULL);
@@ -405,6 +418,10 @@ static void vioapic_deliver(struct hvm_vioapic *vioapic, unsigned int pin)
 
     ASSERT(spin_is_locked(&d->arch.hvm.irq_lock));
 
+    if ( irq == TRACK_IRQ )
+            debugtrace_printk("vIO-APIC deliver irq %u vector %u\n",
+                              irq, vector);
+
     HVM_DBG_LOG(DBG_LEVEL_IOAPIC,
                 "dest=%x dest_mode=%x delivery_mode=%x "
                 "vector=%x trig_mode=%x",
diff --git a/xen/arch/x86/io_apic.c b/xen/arch/x86/io_apic.c
index 49bd778484..db7167eb4b 100644
--- a/xen/arch/x86/io_apic.c
+++ b/xen/arch/x86/io_apic.c
@@ -1641,6 +1641,9 @@ static void mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
     unsigned long v;
     int i;
 
+    if ( desc->irq == TRACK_IRQ )
+        debugtrace_printk("ACK irq %u\n", desc->irq);
+
     irq_complete_move(desc);
 
     if ( !directed_eoi_enabled )
@@ -1688,6 +1691,9 @@ static void mask_and_ack_level_ioapic_irq(struct irq_desc *desc)
 
 static void end_level_ioapic_irq_old(struct irq_desc *desc, u8 vector)
 {
+    if ( desc->irq == TRACK_IRQ )
+        debugtrace_printk("END irq %u\n", desc->irq);
+
     if ( directed_eoi_enabled )
     {
         if ( !(desc->status & (IRQ_DISABLED|IRQ_MOVE_PENDING)) )
diff --git a/xen/arch/x86/irq.c b/xen/arch/x86/irq.c
index 8d1f9a9fc6..ec52e44cb7 100644
--- a/xen/arch/x86/irq.c
+++ b/xen/arch/x86/irq.c
@@ -1109,6 +1109,10 @@ static void irq_guest_eoi_timer_fn(void *data)
     unsigned int i, irq = desc - irq_desc;
     irq_guest_action_t *action;
 
+    if ( desc->irq == TRACK_IRQ )
+        debugtrace_printk("irq_guest_eoi_timer_fn irq %u status %x\n",
+                          desc->irq, desc->status);
+
     spin_lock_irq(&desc->lock);
     
     if ( !(desc->status & IRQ_GUEST) )
@@ -1118,6 +1122,10 @@ static void irq_guest_eoi_timer_fn(void *data)
 
     ASSERT(action->ack_type != ACKTYPE_NONE);
 
+    if ( desc->irq == TRACK_IRQ )
+        debugtrace_printk("ack_type %u in_flight %u\n",
+                          action->ack_type, action->in_flight);
+
     /*
      * Is no IRQ in flight at all, or another instance of this timer already
      * running? Skip everything to avoid forcing an EOI early.
@@ -1837,6 +1845,12 @@ static void do_IRQ_guest(struct irq_desc *desc, unsigned int vector)
     unsigned int        i;
     struct pending_eoi *peoi = this_cpu(pending_eoi);
 
+    if ( desc->irq == TRACK_IRQ )
+        debugtrace_printk("do_IRQ_guest irq %u nr_guests %u ack_type %u in_flight %u\n",
+                          desc->irq, action->nr_guests, action->ack_type,
+                          action->in_flight);
+
+
     if ( unlikely(!action->nr_guests) )
     {
         /* An interrupt may slip through while freeing an ACKTYPE_EOI irq. */
diff --git a/xen/common/debugtrace.c b/xen/common/debugtrace.c
index f3794b9453..b22c09297d 100644
--- a/xen/common/debugtrace.c
+++ b/xen/common/debugtrace.c
@@ -130,14 +130,14 @@ static void debugtrace_toggle(void)
 
 void debugtrace_dump(void)
 {
-    unsigned long flags;
+    //unsigned long flags;
 
     watchdog_disable();
-    spin_lock_irqsave(&debugtrace_lock, flags);
+    //spin_lock_irqsave(&debugtrace_lock, flags);
 
     debugtrace_dump_worker();
 
-    spin_unlock_irqrestore(&debugtrace_lock, flags);
+    //spin_unlock_irqrestore(&debugtrace_lock, flags);
     watchdog_enable();
 }
 
@@ -152,7 +152,10 @@ static void debugtrace_add_to_buf(char *buf)
     {
         data->buf[data->prd++] = *p;
         if ( data->prd == debugtrace_bytes )
+        {
+            panic("END of buffer\n");
             data->prd = 0;
+        }
     }
 }
 
diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
index 6b1305a3e5..e0949b7057 100644
--- a/xen/drivers/passthrough/io.c
+++ b/xen/drivers/passthrough/io.c
@@ -174,7 +174,10 @@ static void pt_irq_time_out(void *data)
          * In the identity mapped case the EOI can also be done now, this way
          * the iteration over the list of domain pirqs is avoided.
          */
-        hvm_gsi_deassert(irq_map->dom, dpci_pirq(irq_map)->pirq);
+        if ( dpci_pirq(irq_map)->pirq == TRACK_IRQ )
+            debugtrace_printk("pt_irq_time_out irq %u\n",
+                              dpci_pirq(irq_map)->pirq);
+        //hvm_gsi_deassert(irq_map->dom, dpci_pirq(irq_map)->pirq);
         irq_map->flags |= HVM_IRQ_DPCI_EOI_LATCH;
         pt_irq_guest_eoi(irq_map->dom, irq_map, NULL);
         spin_unlock(&irq_map->dom->event_lock);
@@ -828,6 +831,9 @@ int hvm_do_IRQ_dpci(struct domain *d, struct pirq *pirq)
          !pirq_dpci || !(pirq_dpci->flags & HVM_IRQ_DPCI_MAPPED) )
         return 0;
 
+    if ( pirq->pirq == TRACK_IRQ )
+        debugtrace_printk("hvm_do_IRQ_dpci irq %u\n", pirq->pirq);
+
     pirq_dpci->masked = 1;
     raise_softirq_for(pirq_dpci);
     return 1;
@@ -1010,6 +1016,10 @@ void hvm_dpci_eoi(struct domain *d, unsigned int guest_gsi,
     if ( !is_iommu_enabled(d) )
         return;
 
+    if ( guest_gsi == TRACK_IRQ )
+        debugtrace_printk("hvm_dpci_eoi irq %u irr %u\n", guest_gsi,
+                          ent->fields.remote_irr);
+
     if ( is_hardware_domain(d) )
     {
         spin_lock(&d->event_lock);
diff --git a/xen/include/xen/irq.h b/xen/include/xen/irq.h
index 43d567fe44..91579c33b9 100644
--- a/xen/include/xen/irq.h
+++ b/xen/include/xen/irq.h
@@ -174,4 +174,6 @@ unsigned int arch_hwdom_irqs(domid_t);
 void arch_evtchn_bind_pirq(struct domain *, int pirq);
 #endif
 
+#define TRACK_IRQ 17
+
 #endif /* __XEN_IRQ_H__ */
-- 
2.29.2