dpci: move from an hvm_irq_dpci (and struct domain) to an hvm_dirq_dpci model

When an interrupt for an PCI (or PCIe) passthrough device is to be sent
to a guest, we find the appropiate 'hvm_dirq_dpci' structure for the
interrupt (PIRQ), set a bit (masked), and schedule an tasklet.

Then the 'hvm_dirq_assist' tasklet gets called with the 'struct domain'
from where it iterates over the the radix-tree of 'hvm_dirq_dpci' (from
zero to the number of PIRQs allocated) which are masked to the guest
and calls each 'hvm_pirq_assist'. If the PIRQ has a bit set (masked) it
figures out how to inject the PIRQ to the guest.

This is inefficient and not fair as:
 - We iterate starting at PIRQ 0 and up every time. That means the PCIe
   devices that have lower PIRQs get to be called first.
 - If we have many PCIe devices passed in with many PIRQs and if most
   of the time only the highest numbered PIRQ get an interrupt (as the
   initial ones are for control) we end up iterating over many PIRQs.

But we could do beter - the 'hvm_dirq_dpci' has the field for
'struct domain', which we can use instead of having to pass in the
'struct domain'.

As such this patch moves the tasklet to the 'struct hvm_dirq_dpci' and
sets the 'dom' field to the domain. We also double-check that the
'->dom' is not reset before using it.

We have to be careful with this as that means we MUST have 'dom' set
before pirq_guest_bind() is called. As such we add the
'pirq_dpci->dom = d;' to cover for such cases.

The mechanism to tear it down is more complex as there are two ways it
can be executed:

 a) pci_clean_dpci_irq. This gets called when the guest is being
    destroyed. We end up calling 'tasklet_kill'.

    The scenarios in which the 'struct pirq' (and subsequently the
    'hvm_pirq_dpci') gets destroyed is when:

    - guest did not use the pirq at all after setup.
    - guest did use pirq, but decided to mask and left it in that
      state.
    - guest did use pirq, but crashed.

    In all of those scenarios we end up calling 'tasklet_kill' which
    will spin on the tasklet if it is running.

 b) pt_irq_destroy_bind (guest disables the MSI). We double-check that
    the softirq has run by piggy-backing on the existing
    'pirq_cleanup_check' mechanism which calls 'pt_pirq_cleanup_check'.
    We add the extra call to 'pt_pirq_softirq_active' in
    'pt_pirq_cleanup_check'.

    NOTE: Guests that use event channels unbind first the event channel
    from PIRQs, so the 'pt_pirq_cleanup_check' won't be called as event
    is set to zero. In that case we either clean it up via the a)
    mechanism. It is OK to re-use the tasklet when 'pt_irq_create_bind'
    is called afterwards.

    There is an extra scenario regardless of event being set or not:
    the guest did 'pt_irq_destroy_bind' while an interrupt was
    triggered and tasklet was scheduled (but had not been run). It is
    OK to still run the tasklet as hvm_dirq_assist won't do anything
    (as the flags are set to zero). As such we can exit out of
    hvm_dirq_assist without doing anything.

Suggested-by: Jan Beulich <jbeulich@suse.com>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>

diff --git a/xen/drivers/passthrough/io.c b/xen/drivers/passthrough/io.c
index 4cd32b5985663a05ff54173eedb9a5652635a720..dceb17e8ad63cfee8ff8ecb4f978bf06e0a7947a 100644 (file)
--- a/xen/drivers/passthrough/io.c
+++ b/xen/drivers/passthrough/io.c
@@ -27,7 +27,7 @@
 #include <xen/hvm/irq.h>
 #include <xen/tasklet.h>
 
-static void hvm_dirq_assist(unsigned long _d);
+static void hvm_dirq_assist(unsigned long arg);
 
 bool_t pt_irq_need_timer(uint32_t flags)
 {
@@ -114,9 +114,6 @@ int pt_irq_create_bind(
             spin_unlock(&d->event_lock);
             return -ENOMEM;
         }
-        softirq_tasklet_init(
-            &hvm_irq_dpci->dirq_tasklet,
-            hvm_dirq_assist, (unsigned long)d);
         for ( i = 0; i < NR_HVM_IRQS; i++ )
             INIT_LIST_HEAD(&hvm_irq_dpci->girq[i]);
 
@@ -144,6 +141,18 @@ int pt_irq_create_bind(
                                HVM_IRQ_DPCI_GUEST_MSI;
             pirq_dpci->gmsi.gvec = pt_irq_bind->u.msi.gvec;
             pirq_dpci->gmsi.gflags = pt_irq_bind->u.msi.gflags;
+            /*
+             * 'pt_irq_create_bind' can be called after 'pt_irq_destroy_bind'.
+             * The 'pirq_cleanup_check' which would free the structure is only
+             * called if the event channel for the PIRQ is active. However
+             * OS-es that use event channels usually bind PIRQs to eventds
+             * and unbind them before calling 'pt_irq_destroy_bind' - with the
+             * result that we re-use the 'dpci' structure. This can be
+             * reproduced with unloading and loading the driver for a device.
+             *
+             * As such on every 'pt_irq_create_bind' call we MUST set it.
+             */
+            pirq_dpci->dom = d;
             /* bind after hvm_irq_dpci is setup to avoid race with irq handler*/
             rc = pirq_guest_bind(d->vcpu[0], info, 0);
             if ( rc == 0 && pt_irq_bind->u.msi.gtable )
@@ -156,6 +165,7 @@ int pt_irq_create_bind(
             {
                 pirq_dpci->gmsi.gflags = 0;
                 pirq_dpci->gmsi.gvec = 0;
+                pirq_dpci->dom = NULL;
                 pirq_dpci->flags = 0;
                 pirq_cleanup_check(info, d);
                 spin_unlock(&d->event_lock);
@@ -232,6 +242,7 @@ int pt_irq_create_bind(
         {
             unsigned int share;
 
+            /* MUST be set, as the pirq_dpci can be re-used. */
             pirq_dpci->dom = d;
             if ( pt_irq_bind->irq_type == PT_IRQ_TYPE_MSI_TRANSLATE )
             {
@@ -415,11 +426,18 @@ void pt_pirq_init(struct domain *d, struct hvm_pirq_dpci *dpci)
 {
     INIT_LIST_HEAD(&dpci->digl_list);
     dpci->gmsi.dest_vcpu_id = -1;
+    softirq_tasklet_init(&dpci->tasklet, hvm_dirq_assist, (unsigned long)dpci);
 }
 
 bool_t pt_pirq_cleanup_check(struct hvm_pirq_dpci *dpci)
 {
-    return !dpci->flags;
+    if ( !dpci->flags )
+    {
+        tasklet_kill(&dpci->tasklet);
+        dpci->dom = NULL;
+        return 1;
+    }
+    return 0;
 }
 
 int pt_pirq_iterate(struct domain *d,
@@ -459,7 +477,7 @@ int hvm_do_IRQ_dpci(struct domain *d, struct pirq *pirq)
         return 0;
 
     pirq_dpci->masked = 1;
-    tasklet_schedule(&dpci->dirq_tasklet);
+    tasklet_schedule(&pirq_dpci->tasklet);
     return 1;
 }
 
@@ -513,9 +531,27 @@ void hvm_dpci_msi_eoi(struct domain *d, int vector)
     spin_unlock(&d->event_lock);
 }
 
-static int _hvm_dirq_assist(struct domain *d, struct hvm_pirq_dpci *pirq_dpci,
-                            void *arg)
+static void hvm_dirq_assist(unsigned long arg)
 {
+    struct hvm_pirq_dpci *pirq_dpci = (struct hvm_pirq_dpci *)arg;
+    struct domain *d = pirq_dpci->dom;
+
+    /*
+     * We can be racing with 'pt_irq_destroy_bind' - with us being scheduled
+     * right before 'pirq_guest_unbind' gets called - but us not yet executed.
+     *
+     * And '->dom' gets cleared later in the destroy path. We exit and clear
+     * 'masked' - which is OK as later in this code we would
+     * do nothing except clear the ->masked field anyhow.
+     */
+    if ( !d )
+    {
+        pirq_dpci->masked = 0;
+        return;
+    }
+    ASSERT(d->arch.hvm_domain.irq.dpci);
+
+    spin_lock(&d->event_lock);
     if ( test_and_clear_bool(pirq_dpci->masked) )
     {
         struct pirq *pirq = dpci_pirq(pirq_dpci);
@@ -526,13 +562,17 @@ static int _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 )
-                return 0;
+            {
+                spin_unlock(&d->event_lock);
+                return;
+            }
         }
 
         if ( pirq_dpci->flags & HVM_IRQ_DPCI_GUEST_MSI )
         {
             vmsi_deliver_pirq(d, pirq_dpci);
-            return 0;
+            spin_unlock(&d->event_lock);
+            return;
         }
 
         list_for_each_entry ( digl, &pirq_dpci->digl_list, list )
@@ -545,7 +585,8 @@ static int _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);
-            return 0;
+            spin_unlock(&d->event_lock);
+            return;
         }
 
         /*
@@ -558,18 +599,6 @@ static int _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);
     }
-
-    return 0;
-}
-
-static void hvm_dirq_assist(unsigned long _d)
-{
-    struct domain *d = (struct domain *)_d;
-
-    ASSERT(d->arch.hvm_domain.irq.dpci);
-
-    spin_lock(&d->event_lock);
-    pt_pirq_iterate(d, _hvm_dirq_assist, NULL);
     spin_unlock(&d->event_lock);
 }
 

diff --git a/xen/drivers/passthrough/pci.c b/xen/drivers/passthrough/pci.c
index 1eba8332c4da1187fe6b5bfa67b578e11874892e..81e8a3af009386fa7f98d6b976d3a49daf817257 100644 (file)
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -767,6 +767,8 @@ static int pci_clean_dpci_irq(struct domain *d,
         xfree(digl);
     }
 
+    tasklet_kill(&pirq_dpci->tasklet);
+
     return 0;
 }
 
@@ -784,8 +786,6 @@ static void pci_clean_dpci_irqs(struct domain *d)
     hvm_irq_dpci = domain_get_irq_dpci(d);
     if ( hvm_irq_dpci != NULL )
     {
-        tasklet_kill(&hvm_irq_dpci->dirq_tasklet);
-
         pt_pirq_iterate(d, pci_clean_dpci_irq, NULL);
 
         d->arch.hvm_domain.irq.dpci = NULL;

diff --git a/xen/include/xen/hvm/irq.h b/xen/include/xen/hvm/irq.h
index c89f4b158ffc2b202b582471dee261d070e36e61..94a550a1892051aba2c73573e73696d03482cf0c 100644 (file)
--- a/xen/include/xen/hvm/irq.h
+++ b/xen/include/xen/hvm/irq.h
@@ -88,7 +88,6 @@ struct hvm_irq_dpci {
     DECLARE_BITMAP(isairq_map, NR_ISAIRQS);
     /* Record of mapped Links */
     uint8_t link_cnt[NR_LINK];
-    struct tasklet dirq_tasklet;
 };
 
 /* Machine IRQ to guest device/intx mapping. */
@@ -100,6 +99,7 @@ struct hvm_pirq_dpci {
     struct domain *dom;
     struct hvm_gmsi_info gmsi;
     struct timer timer;
+    struct tasklet tasklet;
 };
 
 void pt_pirq_init(struct domain *, struct hvm_pirq_dpci *);