[PATCH v2] xen: introduce HVM_PARAM_BUFIOREQ_EVTCHN

[<stefano.stabellini@eu.citrix.com>]

From: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

Introduce an event channel for buffered io event notifications,
advertise the port number using an hvm param.
This way the device model is not forced to check the buffered io page
for data several times a second for the entire life of the VM (buffered
io is mostly used for stdvga emulation in Xen that is switched off after
the guest goes into graphical mode).


Changes in v2:

- return -EINVAL to callers that try to set HVM_PARAM_BUFIOREQ_EVTCHN
from outside the hypervisor.


Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
---
 xen/arch/x86/hvm/hvm.c          |   13 +++++++++++++
 xen/arch/x86/hvm/io.c           |    2 ++
 xen/include/public/hvm/params.h |    3 ++-
 3 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ab7763b..86627f6 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -972,6 +972,16 @@ int hvm_vcpu_initialise(struct vcpu *v)
 
     /* Register ioreq event channel. */
     v->arch.hvm_vcpu.xen_port = rc;
+
+    if ( v->vcpu_id == 0 )
+    {
+        /* Create bufioreq event channel. */
+        rc = alloc_unbound_xen_event_channel(v, 0);
+        if ( rc < 0 )
+            goto fail2;
+        v->domain->arch.hvm_domain.params[HVM_PARAM_BUFIOREQ_EVTCHN] = rc;
+    }
+
     spin_lock(&v->domain->arch.hvm_domain.ioreq.lock);
     if ( v->domain->arch.hvm_domain.ioreq.va != NULL )
         get_ioreq(v)->vp_eport = v->arch.hvm_vcpu.xen_port;
@@ -3543,6 +3553,9 @@ long do_hvm_op(unsigned long op, XEN_GUEST_HANDLE(void) arg)
                         if ( rc == 0 )
                             rc = nestedhvm_vcpu_initialise(v);
                 break;
+            case HVM_PARAM_BUFIOREQ_EVTCHN:
+                rc = -EINVAL;
+                break;
             }
 
             if ( rc == 0 ) 
diff --git a/xen/arch/x86/hvm/io.c b/xen/arch/x86/hvm/io.c
index 7ebefc7..41a2ede 100644
--- a/xen/arch/x86/hvm/io.c
+++ b/xen/arch/x86/hvm/io.c
@@ -118,6 +118,8 @@ int hvm_buffered_io_send(ioreq_t *p)
     wmb();
     pg->write_pointer += qw ? 2 : 1;
 
+    notify_via_xen_event_channel(v->domain,
+            v->domain->arch.hvm_domain.params[HVM_PARAM_BUFIOREQ_EVTCHN]);
     spin_unlock(&iorp->lock);
     
     return 1;
diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 1c5a1a9..6699788 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -52,6 +52,7 @@
 #define HVM_PARAM_IOREQ_PFN    5
 
 #define HVM_PARAM_BUFIOREQ_PFN 6
+#define HVM_PARAM_BUFIOREQ_EVTCHN 26
 
 #ifdef __ia64__
 
@@ -141,6 +142,6 @@
 /* Boolean: Enable nestedhvm (hvm only) */
 #define HVM_PARAM_NESTEDHVM    24
 
-#define HVM_NR_PARAMS          26
+#define HVM_NR_PARAMS          27
 
 #endif /* __XEN_PUBLIC_HVM_PARAMS_H__ */
-- 
1.7.2.3