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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH v6 09/10] tools/arm: tee: add "tee" option for xl.cfg
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. >> >>>> +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. -- Best regards, Volodymyr Babchuk _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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