xen/xenpaging.notify_policy_only_once.patch

Subject: xenpaging: notify policy only on resume

If a page is requested more than once, the policy is also notified more
than once about the page-in. However, a page-in happens only once. Any
further resume will only unpause the other vcpu. The multiple notify
will put the page into the mru list multiple times and it will unlock
other already resumed pages too early. In the worst case, a page that
was just resumed can be evicted right away, causing a deadlock in the
guest.  

(xen-unstable changeset:   22441:7d2c013727d7)

Signed-off-by: Olaf Hering <olaf@aepfle.de>

---
 tools/xenpaging/xenpaging.c |    9 +++++----
 1 file changed, 5 insertions(+), 4 deletions(-)

Index: xen-4.0.2-testing/tools/xenpaging/xenpaging.c
===================================================================
--- xen-4.0.2-testing.orig/tools/xenpaging/xenpaging.c
+++ xen-4.0.2-testing/tools/xenpaging/xenpaging.c
@@ -381,7 +381,7 @@ int xenpaging_evict_page(xenpaging_t *pa
     return ret;
 }
 
-static int xenpaging_resume_page(xenpaging_t *paging, mem_event_response_t *rsp)
+static int xenpaging_resume_page(xenpaging_t *paging, mem_event_response_t *rsp, int notify_policy)
 {
     int ret;
 
@@ -391,7 +391,8 @@ static int xenpaging_resume_page(xenpagi
         goto out;
 
     /* Notify policy of page being paged in */
-    policy_notify_paged_in(paging->mem_event.domain_id, rsp->gfn);
+    if ( notify_policy )
+        policy_notify_paged_in(paging->mem_event.domain_id, rsp->gfn);
 
     /* Tell Xen page is ready */
     ret = xc_mem_paging_resume(paging->xc_handle, paging->mem_event.domain_id,
@@ -622,7 +623,7 @@ int main(int argc, char *argv[])
                 rsp.vcpu_id = req.vcpu_id;
                 rsp.flags = req.flags;
 
-                rc = xenpaging_resume_page(paging, &rsp);
+                rc = xenpaging_resume_page(paging, &rsp, 1);
                 if ( rc != 0 )
                 {
                     ERROR("Error resuming page");
@@ -651,7 +652,7 @@ int main(int argc, char *argv[])
                     rsp.vcpu_id = req.vcpu_id;
                     rsp.flags = req.flags;
 
-                    rc = xenpaging_resume_page(paging, &rsp);
+                    rc = xenpaging_resume_page(paging, &rsp, 0);
                     if ( rc != 0 )
                     {
                         ERROR("Error resuming");