[Xen-devel] [PATCH v15 01/11] multicall: add no preemption ability between two calls

[Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>]

Add a flag to indicate if the execution can be preempted between two
calls. If not specified, stay preemptable.

Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
---
 xen/common/multicall.c   |    5 ++++-
 xen/include/public/xen.h |    4 ++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/xen/common/multicall.c b/xen/common/multicall.c
index fa9d910..83b96eb 100644
--- a/xen/common/multicall.c
+++ b/xen/common/multicall.c
@@ -40,6 +40,7 @@ do_multicall(
     struct mc_state *mcs = &current->mc_state;
     uint32_t         i;
     int              rc = 0;
+    bool_t           preemptable = 0;
 
     if ( unlikely(__test_and_set_bit(_MCSF_in_multicall, &mcs->flags)) )
     {
@@ -52,7 +53,7 @@ do_multicall(
 
     for ( i = 0; !rc && i < nr_calls; i++ )
     {
-        if ( i && hypercall_preempt_check() )
+        if ( preemptable && hypercall_preempt_check() )
             goto preempted;
 
         if ( unlikely(__copy_from_guest(&mcs->call, call_list, 1)) )
@@ -61,6 +62,8 @@ do_multicall(
             break;
         }
 
+        preemptable = mcs->call.flags & MC_NO_PREEMPT;
+
         trace_multicall_call(&mcs->call);
 
         do_multicall_call(&mcs->call);
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index a6a2092..3f8b908 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -550,10 +550,14 @@ DEFINE_XEN_GUEST_HANDLE(mmu_update_t);
 struct multicall_entry {
     xen_ulong_t op, result;
     xen_ulong_t args[6];
+    uint32_t flags;
 };
 typedef struct multicall_entry multicall_entry_t;
 DEFINE_XEN_GUEST_HANDLE(multicall_entry_t);
 
+/* These flags passed in the 'flags' field of multicall_entry_t. */
+#define MC_NO_PREEMPT    (1<<0)  /* Can't be preempted before next entry? */
+
 #if __XEN_INTERFACE_VERSION__ < 0x00040400
 /*
  * Event channel endpoints per domain (when using the 2-level ABI):
-- 
1.7.9.5


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