Re: [Xen-devel] [PATCH v6 09/10] tools/arm: tee: add "tee" option for xl.cfg

[Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>]

Julien Grall writes:

> On 6/18/19 3:30 PM, Volodymyr Babchuk wrote:
>>
>>
>> Julien Grall writes:
>>
>>> On 18/06/2019 12:19, Volodymyr Babchuk wrote:
>>>>
>>>> Hi Julien,
>>>
>>> Hi,
>>>
>>>>
>>>> Julien Grall writes:
>>>>>> +
>>>>>> +=item B<optee>
>>>>>> +
>>>>>> +Allow a guest to use OP-TEE. Note that a virtualization-aware OP-TEE
>>>>>> +is required for this. If this option is selected, guest will be able
>>>>>
>>>>> OOI, what happen if OP-TEE does not support virtualization. Will Xen
>>>>> forbid to use it?
>>>> Yes, Xen will get an error from OP-TEE during domain construction. This
>>>> will lead to domain creation failure.
>>>
>>> This is a bit odd. It means we have no way to know in advance whether
>>> OP-TEE will be able to create a client.
>> Yes. There can be at least two reasons for this:
>> 1. OP-TEE is built without virtualization support at all
>> 2. OP-TEE have no resources for a new guest
>>
>>> In other word, when the
>>> mediator is built in Xen, all existing setup with OP-TEE (and
>>> no-virtualization) will fail.
>> Right. If user provides DTB with 'optee' node, but OP-TEE is build without
>> virtualization support, Dom0 will not be created. This can be fixed by
>> adding new capability flag into OP-TEE, that tells Xen about
>> virtualization support. For some reason I missed this when I implemented
>> VM support in OP-TEE :(
>>
>>> My expectation is Xen should be able to know whether the mediator can be used.
>> I need to implement additional capability flag in the OP-TEE. This is
>> not so hard, but it will be available only in the next release. For now,
>> we can document this limitation somewhere.
>
> Is OP-TEE already released with virtualization? If not, when will it be?
Yes, OP-TEE 3.5.0 was released on 26 April 2019 and it includes
virtualization support.

>>
>>>>
>>>>>> +to access to the real OP-TEE OS running on the host. Guest creation
>>>>>
>>>>> s/real// it is redundant with the rest of the sentence. However, it
>>>>> does not really answer to the question regarding isolation.
>>>> Your assumption is correct - OP-TEE provides isolation on its side.
>>>>
>>>>>
>>>>>> +will fail if OP-TEE have no resources for a new guest. Number of supported
>>>>>> +guests depends on OP-TEE configuration.
>>>>>
>>>>> How about the following description (correct me if my understanding is
>>>>> wrong):
>>>>>
>>>>> "Allow a guest to access the host OP-TEE OS. Xen will mediate the
>>>>> access to OP-TEE and the resource isolation will be provided directly
>>>>> by OP-TEE. OP-TEE itself may limit the number of guests that can
>>>>> concurrently use it. This requires a virtualization-aware OP-TEE for
>>>>> this to work.
>>>>>
>>>>> This feature is a B<technology preview>."
>>>> That's much better than my version. Thank you.
>>>>
>>>>> How can a user know whether OP-TEE supports virtualization? Is it
>>>>> configurable at build?
>>>> Yes, there is a special configuration option CFG_VIRTUALIZATION. This is
>>>> covered in OP-TEE documentation at [1]
>>>>
>>>> [1] https://optee.readthedocs.io/architecture/virtualization.html
>>>
>>> Do we expect the link to be stable? If so, then I think a link in the
>>> documentation would be useful.
>> This is the official OP-TEE documentation. So, yes, it should be stable.
>> I can put this link into the code somewhere.
>
> I would add the link in the xl documentation and also in the commit
> message of patch #2. I can do the later on commit.
It would be great. Thank you.


-- 
Best regards,Volodymyr Babchuk
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