xen: add batch completion callbacks

This adds a mechanism to register a callback function to be called once
a batch of hypercalls has been issued.  This is typically used to unlock
things which must remain locked until the hypercall has taken place.

[ Stable folks: pre-req for 2.6.23 bugfix "xen: deal with stale cr3
  values when unpinning pagetables" ]

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Cc: Stable Kernel <stable@kernel.org>

2 files changed, 29 insertions, 3 deletions

diff --git a/arch/x86/xen/multicalls.c b/arch/x86/xen/multicalls.c
index c837e8e463db..ce9c4b41f02d 100644
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -32,7 +32,11 @@
 struct mc_buffer {
         struct multicall_entry entries[MC_BATCH];
         u64 args[MC_ARGS];
-        unsigned mcidx, argidx;
+        struct callback {
+                void (*fn)(void *);
+                void *data;
+        } callbacks[MC_BATCH];
+        unsigned mcidx, argidx, cbidx;
 };
 
 static DEFINE_PER_CPU(struct mc_buffer, mc_buffer);
@@ -43,6 +47,7 @@ void xen_mc_flush(void)
         struct mc_buffer *b = &__get_cpu_var(mc_buffer);
         int ret = 0;
         unsigned long flags;
+        int i;
 
         BUG_ON(preemptible());
 
@@ -51,8 +56,6 @@ void xen_mc_flush(void)
         local_irq_save(flags);
 
         if (b->mcidx) {
-                int i;
-
                 if (HYPERVISOR_multicall(b->entries, b->mcidx) != 0)
                         BUG();
                 for (i = 0; i < b->mcidx; i++)
@@ -65,6 +68,13 @@ void xen_mc_flush(void)
 
         local_irq_restore(flags);
 
+        for(i = 0; i < b->cbidx; i++) {
+                struct callback *cb = &b->callbacks[i];
+
+                (*cb->fn)(cb->data);
+        }
+        b->cbidx = 0;
+
         BUG_ON(ret);
 }
 
@@ -88,3 +98,16 @@ struct multicall_space __xen_mc_entry(size_t args)
 
         return ret;
 }
+
+void xen_mc_callback(void (*fn)(void *), void *data)
+{
+        struct mc_buffer *b = &__get_cpu_var(mc_buffer);
+        struct callback *cb;
+
+        if (b->cbidx == MC_BATCH)
+                xen_mc_flush();
+
+        cb = &b->callbacks[b->cbidx++];
+        cb->fn = fn;
+        cb->data = data;
+}
diff --git a/arch/x86/xen/multicalls.h b/arch/x86/xen/multicalls.h
index 5d96a5fa210c..8bae996d99a3 100644
--- a/arch/x86/xen/multicalls.h
+++ b/arch/x86/xen/multicalls.h
@@ -42,4 +42,7 @@ static inline void xen_mc_issue(unsigned mode)
         local_irq_restore(x86_read_percpu(xen_mc_irq_flags));
 }
 
+/* Set up a callback to be called when the current batch is flushed */
+void xen_mc_callback(void (*fn)(void *), void *data);
+
 #endif /* _XEN_MULTICALLS_H */