[PATCH 5 of 5] Ignore memory events with an obviously invalid gfn

[Andres Lagar-Cavilla <andres@lagarcavilla.org>]

 xen/arch/x86/mm/mem_sharing.c  |  2 ++
 xen/arch/x86/mm/p2m.c          |  4 ++++
 xen/include/public/mem_event.h |  7 +++++++
 3 files changed, 13 insertions(+), 0 deletions(-)


Ring semantics require that for every request, a response be put. This
allows consumer to place a dummy response if need be.

Signed-off-by: Andres Lagar-Cavilla <andres@lagarcavilla.org>

diff -r c71f4c5b42f0 -r 790cd814bee8 xen/arch/x86/mm/mem_sharing.c
--- a/xen/arch/x86/mm/mem_sharing.c
+++ b/xen/arch/x86/mm/mem_sharing.c
@@ -303,6 +303,8 @@ int mem_sharing_sharing_resume(struct do
     /* Get all requests off the ring */
     while ( mem_event_get_response(&d->mem_event->share, &rsp) )
     {
+        if ( DUMMY_MEM_EVENT_RSP(&rsp) )
+            continue;
         /* Unpause domain/vcpu */
         if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED )
             vcpu_unpause(d->vcpu[rsp.vcpu_id]);
diff -r c71f4c5b42f0 -r 790cd814bee8 xen/arch/x86/mm/p2m.c
--- a/xen/arch/x86/mm/p2m.c
+++ b/xen/arch/x86/mm/p2m.c
@@ -1069,6 +1069,8 @@ void p2m_mem_paging_resume(struct domain
     /* Pull all responses off the ring */
     while( mem_event_get_response(&d->mem_event->paging, &rsp) )
     {
+        if ( DUMMY_MEM_EVENT_RSP(&rsp) )
+            continue;
         /* Fix p2m entry if the page was not dropped */
         if ( !(rsp.flags & MEM_EVENT_FLAG_DROP_PAGE) )
         {
@@ -1177,6 +1179,8 @@ void p2m_mem_access_resume(struct domain
     /* Pull all responses off the ring */
     while( mem_event_get_response(&d->mem_event->access, &rsp) )
     {
+        if ( DUMMY_MEM_EVENT_RSP(&rsp) )
+            continue;
         /* Unpause domain */
         if ( rsp.flags & MEM_EVENT_FLAG_VCPU_PAUSED )
             vcpu_unpause(d->vcpu[rsp.vcpu_id]);
diff -r c71f4c5b42f0 -r 790cd814bee8 xen/include/public/mem_event.h
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -76,6 +76,13 @@ typedef struct mem_event_st {
 
 DEFINE_RING_TYPES(mem_event, mem_event_request_t, mem_event_response_t);
 
+#define INVALID_RSP_GFN -1UL
+
+#define DUMMY_MEM_EVENT_RSP(_r)         ((_r)->gfn == INVALID_RSP_GFN)
+#define MAKE_MEM_EVENT_RSP_DUMMY(_r)    ((_r)->gfn = INVALID_RSP_GFN)
+#define DECLARE_DUMMY_MEM_EVENT_RSP(_name) \
+    mem_event_response_t _name = { .gfn = INVALID_RSP_GFN }
+
 #endif
 
 /*