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 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? :)

Thanks
Yu



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