[PATCH v7 2/3] xen/events: modify struct evtchn layout

[Juergen Gross <jgross@xxxxxxxx>]

In order to avoid latent races when updating an event channel put
xen_consumer and pending fields in different bytes.

At the same time move some other fields around to have less implicit
paddings and to keep related fields more closely together.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 xen/include/xen/sched.h | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index a345cc01f8..e6d09aa055 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -80,8 +80,7 @@ extern domid_t hardware_domid;
 #define EVTCHNS_PER_GROUP  (BUCKETS_PER_GROUP * EVTCHNS_PER_BUCKET)
 #define NR_EVTCHN_GROUPS   DIV_ROUND_UP(MAX_NR_EVTCHNS, EVTCHNS_PER_GROUP)
 
-#define XEN_CONSUMER_BITS 3
-#define NR_XEN_CONSUMERS ((1 << XEN_CONSUMER_BITS) - 1)
+#define NR_XEN_CONSUMERS 8
 
 struct evtchn
 {
@@ -94,9 +93,10 @@ struct evtchn
 #define ECS_VIRQ         5 /* Channel is bound to a virtual IRQ line.        */
 #define ECS_IPI          6 /* Channel is bound to a virtual IPI line.        */
     u8  state;             /* ECS_* */
-    u8  xen_consumer:XEN_CONSUMER_BITS; /* Consumer in Xen if nonzero */
-    u8  pending:1;
-    u16 notify_vcpu_id;    /* VCPU for local delivery notification */
+#ifndef NDEBUG
+    u8  old_state;     /* State when taking lock in write mode. */
+#endif
+    u8  xen_consumer;  /* Consumer in Xen if nonzero */
     u32 port;
     union {
         struct {
@@ -113,11 +113,13 @@ struct evtchn
         } pirq;        /* state == ECS_PIRQ */
         u16 virq;      /* state == ECS_VIRQ */
     } u;
-    u8 priority;
-#ifndef NDEBUG
-    u8 old_state;      /* State when taking lock in write mode. */
-#endif
-    u32 fifo_lastq;    /* Data for fifo events identifying last queue. */
+
+    /* FIFO event channels only. */
+    u8  pending;
+    u8  priority;
+    u16 notify_vcpu_id;    /* VCPU for local delivery notification */
+    u32 fifo_lastq;        /* Data for identifying last queue. */
+
 #ifdef CONFIG_XSM
     union {
 #ifdef XSM_NEED_GENERIC_EVTCHN_SSID
-- 
2.26.2