Re: [Xen-devel] [PATCH 4/8] x86/vm-event/monitor: turn monitor_write_data.do_write into enum

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 04.07.16 at 15:21, <czuzu@xxxxxxxxxxxxxxx> wrote:
> On 7/4/2016 4:07 PM, Jan Beulich wrote:
>>>>> On 04.07.16 at 14:47, <czuzu@xxxxxxxxxxxxxxx> wrote:
>>> On 7/4/2016 3:37 PM, Jan Beulich wrote:
>>>>>>> On 30.06.16 at 20:44, <czuzu@xxxxxxxxxxxxxxx> wrote:
>>>>> After trapping a control-register write vm-event and -until- deciding if 
>>>>> that
>>>>> write is to be permitted or not (VM_EVENT_FLAG_DENY) and doing the actual
>>>>> write,
>>>>> there cannot and should not be another trapped control-register write 
>>>>> event.
>>>> Is that true even for the case where full register state gets updated
>>>> for a vCPU?
>>> AFAIK, the full register state cannot be updated _at once_, that is:
>>> after each trapped register update monitor_write_data must _always_ be
>>> handled _before reentering the vCPU_.
>> I'm thinking about operations like VCPUOP_initialise here. Of course
>> operations on current can't possibly update more than one register
>> at a time.
> 
> Yes but those register update operations happen outside the vm-event 
> subsystem, i.e. in those cases the registers get updated directly, not 
> by setting bits in monitor_write_data.
> Only hypervisor-trapped register updates (e.g. hvm_set_cr0 w/ may_defer 
> parameter = 1) which are deferred because of hvm_event_crX returning 
> true use monitor_write_data.

That's why I had added "Is that updating-all-context case of no
interest to a monitoring application, now and forever?" After all I
gave VCPUOP_initialise as an example because the guest itself
can invoke it, and so I had assumed this to be of interest to a
monitoring app.

Jan


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