[Xen-devel] [PATCH] hvm/monitor: fix usage of the control register mask

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Previous usage is not correct and would prevent certain updates from
being notified to the monitor client.

For example if (value ^ old) == (PGE | PSE) and mask == PGE this
update would not be notified.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Cc: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
Cc: Tamas K Lengyel <tamas@xxxxxxxxxxxxx>
Cc: Jan Beulich <jbeulich@xxxxxxxx>
Cc: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/hvm/monitor.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/arch/x86/hvm/monitor.c b/xen/arch/x86/hvm/monitor.c
index 131b85209f..04665c5f6c 100644
--- a/xen/arch/x86/hvm/monitor.c
+++ b/xen/arch/x86/hvm/monitor.c
@@ -39,7 +39,7 @@ bool hvm_monitor_cr(unsigned int index, unsigned long value, 
unsigned long old)
     if ( (ad->monitor.write_ctrlreg_enabled & ctrlreg_bitmask) &&
          (!(ad->monitor.write_ctrlreg_onchangeonly & ctrlreg_bitmask) ||
           value != old) &&
-         (!((value ^ old) & ad->monitor.write_ctrlreg_mask[index])) )
+         ((value ^ old) & ~ad->monitor.write_ctrlreg_mask[index]) )
     {
         bool sync = ad->monitor.write_ctrlreg_sync & ctrlreg_bitmask;
 
-- 
2.16.1


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