[PATCH V1 11/16] xen/ioreq: Introduce hvm_domain_has_ioreq_server()

[Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>]

From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

This patch introduces a helper the main purpose of which is to check
if a domain is using IOREQ server(s).

On Arm the benefit is to avoid calling handle_hvm_io_completion()
(which implies iterating over all possible IOREQ servers anyway)
on every return in leave_hypervisor_to_guest() if there is no active
servers for the particular domain.

This involves adding an extra per-domain variable to store the count
of servers in use.

Signed-off-by: Julien Grall <julien.grall@xxxxxxx>
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>

---
Please note, this is a split/cleanup/hardening of Julien's PoC:
"Add support for Guest IO forwarding to a device emulator"

Changes RFC -> V1:
   - new patch
---
---
 xen/arch/arm/traps.c             | 15 +++++++++------
 xen/common/ioreq.c               |  9 ++++++++-
 xen/include/asm-arm/domain.h     |  1 +
 xen/include/asm-x86/hvm/domain.h |  1 +
 xen/include/xen/ioreq.h          |  5 +++++
 5 files changed, 24 insertions(+), 7 deletions(-)

diff --git a/xen/arch/arm/traps.c b/xen/arch/arm/traps.c
index 121942c..6b37ae1 100644
--- a/xen/arch/arm/traps.c
+++ b/xen/arch/arm/traps.c
@@ -2263,14 +2263,17 @@ static bool check_for_vcpu_work(void)
     struct vcpu *v = current;
 
 #ifdef CONFIG_IOREQ_SERVER
-    bool handled;
+    if ( hvm_domain_has_ioreq_server(v->domain) )
+    {
+        bool handled;
 
-    local_irq_enable();
-    handled = handle_hvm_io_completion(v);
-    local_irq_disable();
+        local_irq_enable();
+        handled = handle_hvm_io_completion(v);
+        local_irq_disable();
 
-    if ( !handled )
-        return true;
+        if ( !handled )
+            return true;
+    }
 #endif
 
     if ( likely(!v->arch.need_flush_to_ram) )
diff --git a/xen/common/ioreq.c b/xen/common/ioreq.c
index ce12751..4c3a835 100644
--- a/xen/common/ioreq.c
+++ b/xen/common/ioreq.c
@@ -38,9 +38,15 @@ static void set_ioreq_server(struct domain *d, unsigned int 
id,
                              struct hvm_ioreq_server *s)
 {
     ASSERT(id < MAX_NR_IOREQ_SERVERS);
-    ASSERT(!s || !d->arch.hvm.ioreq_server.server[id]);
+    ASSERT((!s && d->arch.hvm.ioreq_server.server[id]) ||
+           (s && !d->arch.hvm.ioreq_server.server[id]));
 
     d->arch.hvm.ioreq_server.server[id] = s;
+
+    if ( s )
+        d->arch.hvm.ioreq_server.nr_servers ++;
+    else
+        d->arch.hvm.ioreq_server.nr_servers --;
 }
 
 /*
@@ -1395,6 +1401,7 @@ unsigned int hvm_broadcast_ioreq(ioreq_t *p, bool 
buffered)
 void hvm_ioreq_init(struct domain *d)
 {
     spin_lock_init(&d->arch.hvm.ioreq_server.lock);
+    d->arch.hvm.ioreq_server.nr_servers = 0;
 
     arch_hvm_ioreq_init(d);
 }
diff --git a/xen/include/asm-arm/domain.h b/xen/include/asm-arm/domain.h
index d1c48d7..0c0506a 100644
--- a/xen/include/asm-arm/domain.h
+++ b/xen/include/asm-arm/domain.h
@@ -31,6 +31,7 @@ struct hvm_domain
     struct {
         spinlock_t              lock;
         struct hvm_ioreq_server *server[MAX_NR_IOREQ_SERVERS];
+        unsigned int            nr_servers;
     } ioreq_server;
 };
 
diff --git a/xen/include/asm-x86/hvm/domain.h b/xen/include/asm-x86/hvm/domain.h
index 765f35c..79e0afb 100644
--- a/xen/include/asm-x86/hvm/domain.h
+++ b/xen/include/asm-x86/hvm/domain.h
@@ -77,6 +77,7 @@ struct hvm_domain {
     struct {
         spinlock_t              lock;
         struct hvm_ioreq_server *server[MAX_NR_IOREQ_SERVERS];
+        unsigned int            nr_servers;
     } ioreq_server;
 
     /* Cached CF8 for guest PCI config cycles */
diff --git a/xen/include/xen/ioreq.h b/xen/include/xen/ioreq.h
index 102f7e8..25ce4c2 100644
--- a/xen/include/xen/ioreq.h
+++ b/xen/include/xen/ioreq.h
@@ -57,6 +57,11 @@ struct hvm_ioreq_server {
     uint8_t                bufioreq_handling;
 };
 
+static inline bool hvm_domain_has_ioreq_server(const struct domain *d)
+{
+    return (d->arch.hvm.ioreq_server.nr_servers > 0);
+}
+
 #define GET_IOREQ_SERVER(d, id) \
     (d)->arch.hvm.ioreq_server.server[id]
 
-- 
2.7.4