Re: [Xen-devel] [PATCH V2] xen/vm_event: Clean up control-register-write vm_events

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Thu, May 14, 2015 at 7:11 PM, Razvan Cojocaru
<rcojocaru@xxxxxxxxxxxxxxx> wrote:
> On 05/14/2015 07:55 PM, Tamas K Lengyel wrote:
>>> diff --git a/xen/include/asm-x86/domain.h b/xen/include/asm-x86/domain.h
>>> index 45b5283..1dd49dd 100644
>>> --- a/xen/include/asm-x86/domain.h
>>> +++ b/xen/include/asm-x86/domain.h
>>> @@ -341,19 +341,13 @@ struct arch_domain
>>>
>>>      /* Monitor options */
>>>      struct {
>>> -        uint16_t mov_to_cr0_enabled          : 1;
>>> -        uint16_t mov_to_cr0_sync             : 1;
>>> -        uint16_t mov_to_cr0_onchangeonly     : 1;
>>> -        uint16_t mov_to_cr3_enabled          : 1;
>>> -        uint16_t mov_to_cr3_sync             : 1;
>>> -        uint16_t mov_to_cr3_onchangeonly     : 1;
>>> -        uint16_t mov_to_cr4_enabled          : 1;
>>> -        uint16_t mov_to_cr4_sync             : 1;
>>> -        uint16_t mov_to_cr4_onchangeonly     : 1;
>>> -        uint16_t mov_to_msr_enabled          : 1;
>>> -        uint16_t mov_to_msr_extended         : 1;
>>> -        uint16_t singlestep_enabled          : 1;
>>> -        uint16_t software_breakpoint_enabled : 1;
>>> +        uint32_t write_ctrlreg_enabled       : 8;
>>> +        uint32_t write_ctrlreg_sync          : 8;
>>> +        uint32_t write_ctrlreg_onchangeonly  : 8;
>>
>> Any particular reason why you have these bitmaps 8-bits wide? There
>> are only 4 events defined at the moment that would use these.
>
> ARM control registers have been mentioned, so I thought I would leave
> some space for a few more events. Other than that, they don't _need_ to
> be 8-bits wide. If compactness matters more I'll change them to 4.
>
>
> Thanks,
> Razvan

IMHO it's better to widen the field when there is an actual need for
it. For now I think 4 would be appropriate.

Thanks,
Tamas

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