Re: [Xen-devel] [PATCH 5 of 5] Ignore memory events with an obviously invalid gfn

["Andres Lagar-Cavilla" <andres@xxxxxxxxxxxxxxxx>]

> At 10:12 -0500 on 05 Dec (1323079924), Andres Lagar-Cavilla wrote:
>>  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.
>>
>> 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
>> +
>
> On a 32-bit system this doesn't do what you want.
>
> Actually, can you use a flag for this, please?  Wedging it into the gfn
> field seems a bit of a hack, and we have plenty of flag bits left.
>
> Tim.

Good point, here it is:

# HG changeset patch
# Parent c71f4c5b42f0c7cc04e4ae758c8ab775305f2c6a
Ignore memory events with an obviously invalid gfn.

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@xxxxxxxxxxxxxxxx>

diff -r c71f4c5b42f0 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 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 xen/include/public/mem_event.h
--- a/xen/include/public/mem_event.h
+++ b/xen/include/public/mem_event.h
@@ -40,6 +40,7 @@
 #define MEM_EVENT_FLAG_DROP_PAGE    (1 << 1)
 #define MEM_EVENT_FLAG_EVICT_FAIL   (1 << 2)
 #define MEM_EVENT_FLAG_FOREIGN      (1 << 3)
+#define MEM_EVENT_FLAG_DUMMY        (1 << 4)

 /* Reasons for the memory event request */
 #define MEM_EVENT_REASON_UNKNOWN     0    /* typical reason */
@@ -76,6 +77,13 @@ typedef struct mem_event_st {

 DEFINE_RING_TYPES(mem_event, mem_event_request_t, mem_event_response_t);

+#define DUMMY_MEM_EVENT_RSP(_r)             \
+        ((_r)->flags & MEM_EVENT_FLAG_DUMMY)
+#define MAKE_MEM_EVENT_RSP_DUMMY(_r)        \
+        ((_r)->flags |= MEM_EVENT_FLAG_DUMMY)
+#define DECLARE_DUMMY_MEM_EVENT_RSP(_name)  \
+    mem_event_response_t _name = { .flags = MEM_EVENT_FLAG_DUMMY }
+
 #endif

 /*



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