Re: [Xen-devel] [PATCH V4] vm_event: Allow subscribing to write events for specific MSR-s

[Tamas K Lengyel <tamas@xxxxxxxxxxxxx>]

>> diff --git a/xen/arch/x86/vm_event.c b/xen/arch/x86/vm_event.c
>> index 5635603..22819c5 100644
>> --- a/xen/arch/x86/vm_event.c
>> +++ b/xen/arch/x86/vm_event.c
>> @@ -20,6 +20,7 @@
>>
>>  #include <xen/sched.h>
>>  #include <asm/hvm/hvm.h>
>> +#include <asm/monitor.h>
>>  #include <asm/vm_event.h>
>>
>>  /* Implicitly serialized by the domctl lock. */
>> @@ -27,6 +28,11 @@ int vm_event_init_domain(struct domain *d)
>>  {
>>      struct vcpu *v;
>>
>> +    d->arch.monitor_msr_bitmap = xzalloc(struct monitor_msr_bitmap);
>> +
>> +    if ( !d->arch.monitor_msr_bitmap )
>> +        return -ENOMEM;
>
> Shouldn't we in principle have a monitor_domain_init() function for
> this, or are monitor and vm_event too intertwined in practice?

I think they are (it doesn't really make sense to try to monitor MSR
writes without initializing the vm_event subsystem). Maybe Tamas has
different ideas?

There is certainly dependency between the two, but it's entirely possible to use vm_event without the monitor subsystem (like for mem_paging and mem_sharing). So +1 for making a monitor_domain_init that get's called only when enabling the MONITOR ring (XEN_DOMCTL_VM_EVENT_OP_MONITOR).

Tamas

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