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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 09.09.16 at 11:56, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:

> 
> On 9/9/2016 5:44 PM, Jan Beulich wrote:
>>>>> On 09.09.16 at 11:24, <yu.c.zhang@xxxxxxxxxxxxxxx> wrote:
>>> On 9/9/2016 4:20 PM, Jan Beulich wrote:
>>>>>>> On 09.09.16 at 09:24, <yu.c.zhang@xxxxxxxxxxxxxxx> 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.

Jan


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