On Fri, Jul 18, 2014 at 9:53 AM, Andrew Cooper <andrew.cooper3@citrix.com> wrote:

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Tested-by: Razvan Cojocaru <rcojocaru@bitdefender.com>

CC: Jan Beulich <JBeulich@suse.com>
CC: Tim Deegan <tim@xen.org>
CC: Andres Lagar-Cavilla <andres@lagarcavilla.org>

CC: Aravindh Puthiyaparambil <aravindp@cisco.com>

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

Couple nits below ...

--
v3:
 * Newline on warning

v2:
 * Allow for multiple pause refcounts
---
 xen/arch/x86/hvm/hvm.c          |    2 +-
 xen/arch/x86/mm/mem_event.c     |   31 +++++++++++++++++++++++++++++++
 xen/arch/x86/mm/mem_sharing.c   |    4 ++--
 xen/arch/x86/mm/p2m.c           |    8 ++++----
 xen/include/asm-x86/mem_event.h |    3 +++
 xen/include/xen/sched.h         |    3 +++
 6 files changed, 44 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
index ef2411c..efd79b8 100644
--- a/xen/arch/x86/hvm/hvm.c
+++ b/xen/arch/x86/hvm/hvm.c
@@ -6113,7 +6113,7 @@ static int hvm_memory_event_traps(long p, uint32_t reason,
     if ( (p & HVMPME_MODE_MASK) == HVMPME_mode_sync )
     {
         req.flags |= MEM_EVENT_FLAG_VCPU_PAUSED;
-        vcpu_pause_nosync(v);
+        mem_event_vcpu_pause(v);
     }

     req.gfn = value;
diff --git a/xen/arch/x86/mm/mem_event.c b/xen/arch/x86/mm/mem_event.c

index 40ae841..ba7e71e 100644

--- a/xen/arch/x86/mm/mem_event.c
+++ b/xen/arch/x86/mm/mem_event.c
@@ -663,6 +663,37 @@ int mem_event_domctl(struct domain *d, xen_domctl_mem_event_op_t *mec,
     return rc;
 }

+void mem_event_vcpu_pause(struct vcpu *v)
+{
+    ASSERT(v == current);
+
+    atomic_inc(&v->mem_event_pause_count);

Nit #1: A buggy toolstack going into an infinite loop could overflow this.

+    vcpu_pause_nosync(v);
+}
+
+void mem_event_vcpu_unpause(struct vcpu *v)
+{
+    int old, new, prev = v->mem_event_pause_count.counter;

Nit #2: not fresh in my mind whether atomic is supposed to be signed or unsigned. The flawless comparison below is to take these all as unsigned and check for new > old.

Thanks

Andres