Re: [Xen-devel] [PATCH v10 09/11] x86/ctxt: Issue a speculation barrier between vcpu contexts

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.01.18 at 17:09, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 25/01/18 15:57, Jan Beulich wrote:
>>>>> On 24.01.18 at 14:12, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> @@ -1743,6 +1744,34 @@ void context_switch(struct vcpu *prev, struct vcpu 
>>> *next)
>>>          }
>>>  
>>>          ctxt_switch_levelling(next);
>>> +
>>> +        if ( opt_ibpb && !is_idle_domain(nextd) )
>> Is the idle domain check here really useful?
> 
> Yes, because as you pointed out in v9, the outer condition isn't
> sufficient to exclude nextd being idle.

True, but then again - what's wrong with an idle vCPU making it
into the block? It'll be a pointless barrier that you issue, but no
other harm afaics. Remember that I complained about the missing
check only because of the chosen variable naming, but you've
renamed the variables in question, so I don't see why you've also
added the extra condition.

Jan


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