Re: [PATCH v9 1/3] x86/tlb: introduce a flush HVM ASIDs flag

[Jan Beulich <jbeulich@suse.com>]

On 08.04.2020 17:10, Roger Pau Monné wrote:
> On Wed, Apr 08, 2020 at 01:25:14PM +0200, Jan Beulich wrote:
>> On 06.04.2020 12:57, Roger Pau Monne wrote:
>>> --- a/xen/arch/x86/mm/paging.c
>>> +++ b/xen/arch/x86/mm/paging.c
>>> @@ -613,7 +613,8 @@ void paging_log_dirty_range(struct domain *d,
>>>  
>>>      p2m_unlock(p2m);
>>>  
>>> -    flush_tlb_mask(d->dirty_cpumask);
>>> +    flush_mask(d->dirty_cpumask, (!hap_enabled(d) ? FLUSH_TLB : 0) |
>>> +                                 FLUSH_HVM_ASID_CORE);
>>
>> In cases where one case is assumed to be more likely than the other
>> putting the more likely one first can be viewed as a mild hint to
>> the compiler, and hence an extra ! may be warranted in an if() or
>> a conditional expression. Here, however, I don't think we can
>> really consider one case more likely than the other, and hence I'd
>> suggest to avoid the !, flipping the other two expressions
>> accordingly. I may take the liberty to adjust this while committing
>> (if I'm to be the one).
> 
> That's fine, thanks. Somehow '!hap -> flush' was clearer in my mind.

Thinking about it with the other HVM-related changes in v9, shouldn't
this then be

    flush_mask(d->dirty_cpumask, (hap_enabled(d) ? 0 : FLUSH_TLB) |
                                 (is_hvm_domain(d) ? FLUSH_HVM_ASID_CORE : 0));

Or wait - the only caller lives in hap.c. As a result the FLUSH_TLB
part can be dropped altogether. And I question the need of flushing
guest TLBs - this is purely a p2m operation. I'll go look at the
history of this function, but for now I think the call should be
dropped (albeit then maybe better in a separate patch).

Jan