hyperv: add synic message delivery

Add infrastructure to deliver SynIC messages to the SynIC message page.

Note that KVM may also want to deliver (SynIC timer) messages to the
same message slot.

The problem is that the access to a SynIC message slot is controlled by
the value of its .msg_type field which indicates if the slot is being
owned by the hypervisor (zero) or by the guest (non-zero).

This leaves no room for synchronizing multiple concurrent producers.

The simplest way to deal with this for both KVM and QEMU is to only
deliver messages in the vcpu thread.  KVM already does this; this patch
makes it for QEMU, too.

Specifically,

 - add a function for posting messages, which only copies the message
   into the staging buffer if its free, and schedules a work on the
   corresponding vcpu to actually deliver it to the guest slot;

 - instead of a sint ack callback, set up the sint route with a message
   status callback.  This function is called in a bh whenever there are
   updates to the message slot status: either the vcpu made definitive
   progress delivering the message from the staging buffer (succeeded or
   failed) or the guest issued EOM; the status is passed as an argument
   to the callback.

Signed-off-by: Roman Kagan <rkagan@virtuozzo.com>
Message-Id: <20180921082217.29481-6-rkagan@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/include/hw/hyperv/hyperv.h b/include/hw/hyperv/hyperv.h
index 6fba4762c8..82d561fc88 100644
--- a/include/hw/hyperv/hyperv.h
+++ b/include/hw/hyperv/hyperv.h
@@ -11,18 +11,30 @@
 #define HW_HYPERV_HYPERV_H
 
 #include "cpu-qom.h"
+#include "hw/hyperv/hyperv-proto.h"
 
 typedef struct HvSintRoute HvSintRoute;
-typedef void (*HvSintAckClb)(void *data);
+
+/*
+ * Callback executed in a bottom-half when the status of posting the message
+ * becomes known, before unblocking the connection for further messages
+ */
+typedef void (*HvSintMsgCb)(void *data, int status);
 
 HvSintRoute *hyperv_sint_route_new(uint32_t vp_index, uint32_t sint,
-                                   HvSintAckClb sint_ack_clb,
-                                   void *sint_ack_clb_data);
+                                   HvSintMsgCb cb, void *cb_data);
 void hyperv_sint_route_ref(HvSintRoute *sint_route);
 void hyperv_sint_route_unref(HvSintRoute *sint_route);
 
 int hyperv_sint_route_set_sint(HvSintRoute *sint_route);
 
+/*
+ * Submit a message to be posted in vcpu context.  If the submission succeeds,
+ * the status of posting the message is reported via the callback associated
+ * with the @sint_route; until then no more messages are accepted.
+ */
+int hyperv_post_msg(HvSintRoute *sint_route, struct hyperv_message *msg);
+
 static inline uint32_t hyperv_vp_index(CPUState *cs)
 {
     return cs->cpu_index;