Re: [Xen-devel] [PATCH v4] x86/mm: Add mem access rights to NPT

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 25.07.18 at 11:25, <george.dunlap@xxxxxxxxxx> wrote:
> On 07/24/2018 01:02 PM, Jan Beulich wrote:
>>>>> On 24.07.18 at 13:26, <george.dunlap@xxxxxxxxxx> wrote:
>>> On 07/24/2018 09:55 AM, Jan Beulich wrote:
>>>>>>> On 23.07.18 at 15:48, <aisaila@xxxxxxxxxxxxxxx> wrote:
>>>>> +        {
>>>>> +            xfree(d->arch.monitor.msr_bitmap);
>>>>> +            return -ENOMEM;
>>>>> +        }
>>>>> +        radix_tree_init(p2m->mem_access_settings);
>>>>> +    }
>>>>
>>>> What's the SVM connection here? Please don't forget that p2m-pt.c
>>>> also serves the shadow case. Perhaps struct p2m_domain should
>>>> contain a boolean indicator whether this auxiliary data structure is
>>>> needed?
>>>
>>> It's basically just "hap_enabled()" isn't it?
>> 
>> Only if we can't make it there when EPT is active.
> 
> It can make it here when VMX is active and shadow is enabled, but it
> shouldn't be able to get here when EPT is active.  We could add an
> ASSERT() to that effect; it should be safe in production, as the only
> side effect should be that we do a small pointless allocation.

So I've looked a little more closely: This is being added to
arch_monitor_init_domain(), called from vm_event_domctl(). I can't
see why this wouldn't be reachable with EPT enabled.

Jan



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