Re: [Xen-devel] [PATCH v6 3/9] xen/x86: support per-domain flag for xpti

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 10.04.18 at 11:32, <jgross@xxxxxxxx> wrote:
> On 10/04/18 11:14, Jan Beulich wrote:
>>>>> On 10.04.18 at 09:58, <jgross@xxxxxxxx> wrote:
>>> --- a/docs/misc/xen-command-line.markdown
>>> +++ b/docs/misc/xen-command-line.markdown
>>> @@ -1955,14 +1955,29 @@ clustered mode.  The default, given no hint from 
>>> the **FADT**, is cluster
>>>  mode.
>>>  
>>>  ### xpti
>>> -> `= <boolean>`
>>> +> `= List of [ default | <boolean> | dom0=<bool> | domu=<bool> ]`
>>>  
>>> -> Default: `false` on AMD hardware
>>> +> Default: `false` on hardware not vulnerable to Meltdown (e.g. AMD)
>>>  > Default: `true` everywhere else
>>>  
>>>  Override default selection of whether to isolate 64-bit PV guest page
>>>  tables.
>>>  
>>> +`true` activates page table isolation even on hardware not vulnerable by
>>> +Meltdown for all domains.
>>> +
>>> +`false` deactivates page table isolation on all systems for all domains.
>>> +
>>> +`default` sets the default behaviour.
>>> +
>>> +`dom0=false` deactivates page table isolation for dom0.
>>> +
>>> +`dom0=true` activates page table isolation for dom0.
>>> +
>>> +`domu=false` deactivates page table isolation for guest domains.
>>> +
>>> +`domu=true` activates page table isolation for guest domains.
>> 
>> This is too verbose / repetitive for my taste.
> 
> So you'd like it better as:
> 
> "With `dom0` and `domu` it is possible to control page table isolation
> for dom0 or guest domains only." ?

Yes.

>>> @@ -205,6 +208,10 @@ int pv_domain_initialise(struct domain *d)
>>>      /* 64-bit PV guest by default. */
>>>      d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 0;
>>>  
>>> +    d->arch.pv_domain.xpti = (d->domain_id == hardware_domid)
>>> +                             ? (opt_xpti & XPTI_DOM0)
>>> +                             : (opt_xpti & XPTI_DOMU);
>> 
>> I would generally prefer to have as little redundancy as possible in
>> such expressions, i.e.
>> 
>>     d->arch.pv_domain.xpti = opt_xpti & (d->domain_id == hardware_domid
>>                                          ? XPTI_DOM0 : XPTI_DOMU);
> 
> Okay.
> 
>> 
>> Furthermore - shouldn't this cover domain 0 as well as the hardware
>> domain, even if - in case they are different - domain 0 should be
>> short lived?
> 
> When domain 0 is created is _is_ the hardware domain. Only domain 0
> creating a hardware domain will set hardware_domid to a non-zero value.

hardware_domid is set by an integer_param() afaics, so would be
set long before creation of domain 0.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel