File xenpaging.evict_fail_fast_forward.patch of Package xen

# HG changeset patch
# Parent 00989d5f44b59ba7f3a467342a14b9c7621fa926
xenpaging: restore p2mt if gfn is needed before evict

In the rare case that a gfn is needed by a guest or a foreign domain
between nominate and evict, restore the p2mt and skip sending a request.
A request is not needed because the pager will notice the evict failure.

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

---
 xen/arch/x86/mm/p2m.c |   18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

Index: xen-4.1.2-testing/xen/arch/x86/mm/p2m.c
===================================================================
--- xen-4.1.2-testing.orig/xen/arch/x86/mm/p2m.c
+++ xen-4.1.2-testing/xen/arch/x86/mm/p2m.c
@@ -3036,6 +3036,7 @@ void p2m_mem_paging_populate(struct p2m_
     p2m_type_t p2mt;
     p2m_access_t a;
     mfn_t mfn;
+    int restored = 0;
     struct domain *d = p2m->domain;
 
     /* Check that there's space on the ring for this request */
@@ -3051,23 +3052,25 @@ void p2m_mem_paging_populate(struct p2m_
     /* Allow only nominated or evicted pages to enter page-in path */
     if ( p2m_do_populate(p2mt) )
     {
-        /* Evict will fail now, tag this request for pager */
-        if ( p2mt == p2m_ram_paging_out )
-            req.flags |= MEM_EVENT_FLAG_EVICT_FAIL;
-
-        set_p2m_entry(p2m, gfn, mfn, 0, p2m_ram_paging_in_start, a);
+        /* Restore page state if gfn was requested before evict */
+        if ( p2mt == p2m_ram_paging_out && mfn_valid(mfn) ) {
+            set_p2m_entry(p2m, gfn, mfn, 0, p2m_ram_rw, a);
+            restored = 1;
+        } else {
+            set_p2m_entry(p2m, gfn, mfn, 0, p2m_ram_paging_in_start, a);
+        }
         audit_p2m(p2m, 1);
     }
     p2m_unlock(p2m);
 
     /* Pause domain if request came from guest and gfn has paging type */
-    if (  p2m_is_paging(p2mt) && v->domain == d )
+    if ( !restored && p2m_is_paging(p2mt) && v->domain == d )
     {
         vcpu_pause_nosync(v);
         req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED;
     }
     /* No need to inform pager if the gfn is not in the page-out path */
-    else if ( !p2m_do_populate(p2mt) )
+    else if ( restored || !p2m_do_populate(p2mt) )
     {
         /* gfn is already on its way back and vcpu is not paused */
         mem_event_put_req_producers(&d->mem_event->paging);