kvm/i386: Add xen-evtchn-max-pirq property

The default number of PIRQs is set to 256 to avoid issues with 32-bit MSI
devices. Allow it to be increased if the user desires.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Reviewed-by: Paul Durrant <paul@xen.org>

6 files changed, 54 insertions, 10 deletions

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 3d8e400..f2a6ea6 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3705,6 +3705,7 @@ static void kvm_accel_instance_init(Object *obj)
     s->notify_window = 0;
     s->xen_version = 0;
     s->xen_gnttab_max_frames = 64;
+    s->xen_evtchn_max_pirq = 256;
 }
 
 /**
diff --git a/hw/i386/kvm/xen_evtchn.c b/hw/i386/kvm/xen_evtchn.c
index 69c0204..886fbf6 100644
--- a/hw/i386/kvm/xen_evtchn.c
+++ b/hw/i386/kvm/xen_evtchn.c
@@ -302,17 +302,18 @@ void xen_evtchn_create(void)
     }
 
     /*
-     * We could parameterise the number of PIRQs available if needed,
-     * but for now limit it to 256. The Xen scheme for encoding PIRQ#
-     * into an MSI message is not compatible with 32-bit MSI, as it
-     * puts the high bits of the PIRQ# into the high bits of the MSI
-     * message address, instead of using the Extended Destination ID
-     * in address bits 4-11 which perhaps would have been a better
-     * choice. So to keep life simple, just stick with 256 as the
-     * default, which conveniently doesn't need to set anything
-     * outside the low 32 bits of the address.
+     * The Xen scheme for encoding PIRQ# into an MSI message is not
+     * compatible with 32-bit MSI, as it puts the high bits of the
+     * PIRQ# into the high bits of the MSI message address, instead of
+     * using the Extended Destination ID in address bits 4-11 which
+     * perhaps would have been a better choice.
+     *
+     * To keep life simple, kvm_accel_instance_init() initialises the
+     * default to 256. which conveniently doesn't need to set anything
+     * outside the low 32 bits of the address. It can be increased by
+     * setting the xen-evtchn-max-pirq property.
      */
-    s->nr_pirqs = 256;
+    s->nr_pirqs = kvm_xen_get_evtchn_max_pirq();
 
     s->nr_pirq_inuse_words = DIV_ROUND_UP(s->nr_pirqs, 64);
     s->pirq_inuse_bitmap = g_new0(uint64_t, s->nr_pirq_inuse_words);
diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
index 39ce4d3..a641c97 100644
--- a/include/sysemu/kvm_int.h
+++ b/include/sysemu/kvm_int.h
@@ -121,6 +121,7 @@ struct KVMState
     uint32_t xen_version;
     uint32_t xen_caps;
     uint16_t xen_gnttab_max_frames;
+    uint16_t xen_evtchn_max_pirq;
 };
 
 void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
diff --git a/include/sysemu/kvm_xen.h b/include/sysemu/kvm_xen.h
index b2aafaf..595abfb 100644
--- a/include/sysemu/kvm_xen.h
+++ b/include/sysemu/kvm_xen.h
@@ -26,6 +26,7 @@ void kvm_xen_inject_vcpu_callback_vector(uint32_t vcpu_id, int type);
 void kvm_xen_set_callback_asserted(void);
 int kvm_xen_set_vcpu_virq(uint32_t vcpu_id, uint16_t virq, uint16_t port);
 uint16_t kvm_xen_get_gnttab_max_frames(void);
+uint16_t kvm_xen_get_evtchn_max_pirq(void);
 
 #define kvm_xen_has_cap(cap) (!!(kvm_xen_get_caps() &           \
                                  KVM_XEN_HVM_CONFIG_ ## cap))
diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
index d390137..1aef54f 100644
--- a/target/i386/kvm/kvm.c
+++ b/target/i386/kvm/kvm.c
@@ -5922,6 +5922,33 @@ static void kvm_arch_set_xen_gnttab_max_frames(Object *obj, Visitor *v,
     s->xen_gnttab_max_frames = value;
 }
 
+static void kvm_arch_get_xen_evtchn_max_pirq(Object *obj, Visitor *v,
+                                             const char *name, void *opaque,
+                                             Error **errp)
+{
+    KVMState *s = KVM_STATE(obj);
+    uint16_t value = s->xen_evtchn_max_pirq;
+
+    visit_type_uint16(v, name, &value, errp);
+}
+
+static void kvm_arch_set_xen_evtchn_max_pirq(Object *obj, Visitor *v,
+                                             const char *name, void *opaque,
+                                             Error **errp)
+{
+    KVMState *s = KVM_STATE(obj);
+    Error *error = NULL;
+    uint16_t value;
+
+    visit_type_uint16(v, name, &value, &error);
+    if (error) {
+        error_propagate(errp, error);
+        return;
+    }
+
+    s->xen_evtchn_max_pirq = value;
+}
+
 void kvm_arch_accel_class_init(ObjectClass *oc)
 {
     object_class_property_add_enum(oc, "notify-vmexit", "NotifyVMexitOption",
@@ -5954,6 +5981,13 @@ void kvm_arch_accel_class_init(ObjectClass *oc)
                               NULL, NULL);
     object_class_property_set_description(oc, "xen-gnttab-max-frames",
                                           "Maximum number of grant table frames");
+
+    object_class_property_add(oc, "xen-evtchn-max-pirq", "uint16",
+                              kvm_arch_get_xen_evtchn_max_pirq,
+                              kvm_arch_set_xen_evtchn_max_pirq,
+                              NULL, NULL);
+    object_class_property_set_description(oc, "xen-evtchn-max-pirq",
+                                          "Maximum number of Xen PIRQs");
 }
 
 void kvm_set_max_apic_id(uint32_t max_apic_id)
diff --git a/target/i386/kvm/xen-emu.c b/target/i386/kvm/xen-emu.c
index 96a9082..bad3131 100644
--- a/target/i386/kvm/xen-emu.c
+++ b/target/i386/kvm/xen-emu.c
@@ -1765,6 +1765,12 @@ uint16_t kvm_xen_get_gnttab_max_frames(void)
     return s->xen_gnttab_max_frames;
 }
 
+uint16_t kvm_xen_get_evtchn_max_pirq(void)
+{
+    KVMState *s = KVM_STATE(current_accel());
+    return s->xen_evtchn_max_pirq;
+}
+
 int kvm_put_xen_state(CPUState *cs)
 {
     X86CPU *cpu = X86_CPU(cs);