[Xen-devel] [PATCH 06/12] xen: add batch completion callbacks

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

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@xxxxxxxxxxxxx>
Cc: Stable Kernel <stable@xxxxxxxxxx>

---
 arch/x86/xen/multicalls.c |   29 ++++++++++++++++++++++++++---
 arch/x86/xen/multicalls.h |    3 +++
 2 files changed, 29 insertions(+), 3 deletions(-)

===================================================================
--- a/arch/x86/xen/multicalls.c
+++ b/arch/x86/xen/multicalls.c
@@ -32,7 +32,11 @@ struct mc_buffer {
 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++)
@@ -64,6 +67,13 @@ void xen_mc_flush(void)
                BUG_ON(b->argidx != 0);
 
        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(si
 
        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;
+}
===================================================================
--- a/arch/x86/xen/multicalls.h
+++ b/arch/x86/xen/multicalls.h
@@ -42,4 +42,7 @@ static inline void xen_mc_issue(unsigned
        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 */

-- 


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