Re: [Xen-devel] [PATCH v8 3/9] xen/x86: support per-domain flag for xpti

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.04.18 at 17:54, <jgross@xxxxxxxx> wrote:
> On 18/04/18 17:45, Jan Beulich wrote:
>>>>> On 18.04.18 at 17:33, <jgross@xxxxxxxx> wrote:
>>> On 18/04/18 17:29, Jan Beulich wrote:
>>>>>>> On 18.04.18 at 10:30, <jgross@xxxxxxxx> wrote:
>>>>> --- a/xen/arch/x86/mm/shadow/multi.c
>>>>> +++ b/xen/arch/x86/mm/shadow/multi.c
>>>>> @@ -967,7 +967,7 @@ static int shadow_set_l4e(struct domain *d,
>>>>>          sh_put_ref(d, osl3mfn, paddr);
>>>>>      }
>>>>>  
>>>>> -    if ( !cpu_has_no_xpti )
>>>>> +    if ( is_pv_domain(d) && d->arch.pv_domain.xpti )
>>>>>          /*
>>>>>           * Lazy flushing is enough: either we do a TLB flush right 
>>>>> afterwards
>>>>>           * which will pick up the new root page table on all affected 
>>>>> cpus
>>>>
>>>> How come the is_pv_domain() is appearing only here?
>>>
>>> It is mandatory for testing the per-domain xpti flag. I could add it in
>>> patch 1 already if you like that better.
>> 
>> Well, if you added it earlier, some unnecessary IPIs would be suppressed
>> right away.
> 
> Which IPIs? There is no IPI involved here. We are just setting the flags
> from the current cpu for all cpus which need to picḱ it up. That's the
> reason for the comment regarding "lazy flushing".

Oh, I did assume flush_root_pgt_mask() would be a function that I had
seen in prior versions, invoking the processing of FLUSH_ROOT_PGTBL on
remote CPUs.

Clearly with the introduction of a new function you should have dropped
my R-b; I'll comment there.

Jan


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