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

[Juergen Gross <jgross@xxxxxxxx>]

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".


Juergen


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