Re: [PATCH v6 4/4] x86/ioreq server: Reset outstanding p2m_ioreq_server entries when an ioreq server unmaps.

[Yu Zhang <yu.c.zhang@linux.intel.com>]

On 9/9/2016 6:09 PM, Jan Beulich wrote:
>>>> On 09.09.16 at 11:56, <yu.c.zhang@linux.intel.com> wrote:
>> On 9/9/2016 5:44 PM, Jan Beulich wrote:
>>>>>> On 09.09.16 at 11:24, <yu.c.zhang@linux.intel.com> wrote:
>>>> On 9/9/2016 4:20 PM, Jan Beulich wrote:
>>>>>>>> On 09.09.16 at 09:24, <yu.c.zhang@linux.intel.com> wrote:
>>>>>> On 9/9/2016 1:26 PM, Yu Zhang wrote:
>>>>>>>>>> On 02.09.16 at 12:47, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>>>>>>> @@ -965,7 +968,8 @@ static mfn_t ept_get_entry(struct p2m_domain *p2m,
>>>>>>>>         if ( is_epte_valid(ept_entry) )
>>>>>>>>         {
>>>>>>>>             if ( (recalc || ept_entry->recalc) &&
>>>>>>>> -             p2m_is_changeable(ept_entry->sa_p2mt) )
>>>>>>>> +             p2m_is_changeable(ept_entry->sa_p2mt) &&
>>>>>>>> +             (ept_entry->sa_p2mt != p2m_ioreq_server) )
>>>>>>>>                 *t = p2m_is_logdirty_range(p2m, gfn, gfn) ?
>>>>>>> p2m_ram_logdirty
>>>>>>>>                                                           : p2m_ram_rw;
>>>>>>>>             else
>>>>>>> Considering this (and at least one more similar adjustment further
>>>>>>> down), is it really appropriate to include p2m_ioreq_server in the
>>>>>>> set of "changeable" types?
>>>>>> Well, I agree p2m_ioreq_server do have different behaviors than the
>>>>>> p2m_log_dirty, but removing p2m_ioreq_server from changeable type
>>>>>> would need more specific code for the p2m_ioreq_server in routines like
>>>>>> resolve_misconfig(), do_recalc() and p2m_change_entry_type_global() etc.
>>>>>> I've tried this approach and abandoned later. :)
>>>>> I can see that the other option might require more adjustments, in
>>>>> which case I guess this variant would be fine if you created another
>>>>> helper (well named) inline function instead of open coding this in
>>>>> several places. Of course such dissimilar handling in the various
>>>>> places p2m_is_changeable() gets used right now will additionally
>>>>> require good reasoning - after all that predicate exists to express
>>>>> the similarities between different code paths.
>>>> Thanks Jan.
>>>> Well, for the logic of p2m type recalculation, similarities between
>>>> p2m_ioreq_server
>>>> and other changeable types exceeds their differences. As to the special
>>>> cases, how
>>>> about we use a macro, i.e. p2m_is_ioreq?
>>> That'd be better than the open coded check, but would still result
>>> in (taking the above example)
>>>
>>>                p2m_is_changeable(ept_entry->sa_p2mt) &&
>>>                !p2m_is_ioreq(ept_entry->sa_p2mt) )
>>>
>>> ? What I'd prefer is a predicate that can be applied here on its own,
>>> without involving && or ||.
>>>
>> OK. I can think of 2 scenarios that p2m_ioreq_server needs special handling:
>>
>> 1> In ept_get_entry()/recal_type(), the p2m types are supposed to return
>> as it is, instead of
>> changing to p2m_log_dirty. So we can use a macro or a inline function
>> like p2m_check_changeable(),
>> which combines the
>>
>>                p2m_is_changeable(ept_entry->sa_p2mt) &&
>>                !p2m_is_ioreq(ept_entry->sa_p2mt) )
>>
>> together.
>>
>> 2> In resolve_misconfig()/do_recalc(), the entry_count gets decremented. We
>> do not need this new inline function, because they are in a separate
>> if() statement.
>>
>> Is this OK? :)
> Sounds reasonable. But please give George and others a chance to
> voice their opinions before you go that route.
>
>

Sure, thanks!

Yu

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