Re: [Xen-devel] [PATCH v2 07/12] x86/altp2m: add control of suppress_ve.

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.06.15 at 18:36, <edmund.h.white@xxxxxxxxx> wrote:
> On 06/25/2015 01:12 AM, Jan Beulich wrote:
>>>>> On 24.06.15 at 19:53, <edmund.h.white@xxxxxxxxx> wrote:
>>> On 06/24/2015 07:38 AM, Jan Beulich wrote:
>>>>>>> On 22.06.15 at 20:56, <edmund.h.white@xxxxxxxxx> wrote:
>>>>> --- a/xen/include/asm-x86/p2m.h
>>>>> +++ b/xen/include/asm-x86/p2m.h
>>>>> @@ -237,6 +237,19 @@ struct p2m_domain {
>>>>>                                         p2m_access_t *p2ma,
>>>>>                                         p2m_query_t q,
>>>>>                                         unsigned int *page_order);
>>>>> +    int                (*set_entry_full)(struct p2m_domain *p2m,
>>>>> +                                         unsigned long gfn,
>>>>> +                                         mfn_t mfn, unsigned int 
>>> page_order,
>>>>> +                                         p2m_type_t p2mt,
>>>>> +                                         p2m_access_t p2ma,
>>>>> +                                         unsigned int sve);
>>>>> +    mfn_t              (*get_entry_full)(struct p2m_domain *p2m,
>>>>> +                                         unsigned long gfn,
>>>>> +                                         p2m_type_t *p2mt,
>>>>> +                                         p2m_access_t *p2ma,
>>>>> +                                         p2m_query_t q,
>>>>> +                                         unsigned int *page_order,
>>>>> +                                         unsigned int *sve);
>>>>
>>>> I have to admit that I find the _full suffixes here pretty odd. Based
>>>> on the functionality, they should be _sve. But then it seems
>>>> questionable how they could be useful to the generic p2m layer
>>>> anyway, i.e. why there would need to be such hooks in the first
>>>> place.
>>>
>>> I did originally use _sve suffixes. I changed them because there
>>> may be some future case where these routines control some other
>>> EPTE bit too. I made them hooks because I thought calling ept...
>>> functions directly would be a layering violation.
>> 
>> Indeed it would. But thinking about it more, I would suggest to
>> extend the existing accessors rather than adding new ones.
>> Just consider what would result when further such return values
>> are going to be needed in the future: I don't see us adding
>> _fuller, _fullest, etc variants. Perhaps just make the new output
>> an optional generic "flags" one. One might even consider folding
>> it with order, or even consolidate all the outputs into a single
>> structure.
> 
> The new functions are called in 3 places only, so changing them
> later would have minimal impact. The existing functions are called
> in many, many places. I *really* don't want to go changing the
> amount of existing code that doing what you suggest would entail
> at this late stage.

I continue to think differently (and I don't consider "at this late
stage" a particularly relevant argument), but the maintainer will
have the final say anyway - George?

Jan


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