[Xen-devel] Xen ARM community call - meeting minutes and date for the next one

[Julien Grall <julien.grall@xxxxxxx>]

Hi all,

Apologies for the late sending. You will find at the end of the mail a summary
of the discussion. Feel free to reply if I missed some parts.

At the end of the call we agreed to have another meeting before the end of the
year. Given that the Christmas is approaching and some people may take holidays
around, I would suggest to do the meeting on Wednesday 14th December at 4pm
UTC. Any opinions?

Also, do you have any specific topic you would like to talk during the next 
call?

Cheers,

== Attendees ==

Apologies if I misspelled any name.

* Stefano Stabellini:
    Aporeto, Xen ARM maintainer
* Julien Grall
    ARM, Xen ARM maintainer
* Artem Mygaiev, Andrii Anisov, Alexandre Agizim:
    EPAM, Embedded and automotive application for Xen
* Steward Hildebrand:
    Dornerworks, help customer to use Xen in their product
* Edgar Iglesias:
    Xilinx, Embedded and datacenter application
* Meng Xu:
    University of Pennsylvania, RT Xen. Looking for improving performance for
    real-time application in virtualised environment
* Bosch (sorry I forgot the name of the attendees): Car multimedia
* Anastassios Nanos:
    OnApp, using Xen on lower power server
* Dario Faggioli:
    Citrix, scheduler maintainer. Interested in following big.LITTLE discussion

== Features ==

=== Co-processor architecture ===

Artem:  EPAM is working on a co-processor framework to share resources between
        guests (see a RFC of the design document [1]). A prototype has been
        created by sharing a GPU between guests, the overhead is ~5% compare
        to native.
Julien: concerned about context switch time
Stefano: concerned about the size of the emulator and security impact
Edgar:  it might not be possible to know the FPGA accelerator when building
        Xen.
Stefano: having the emulator in Xen EL1 would be better for protection
Andrii: it is not necessary to implement a full co-processor emulator. It is
        sufficient to emulation the behavior on register write.

ACTION: Continue the discussion on the mailing list.

=== big.LITTLE ===

Anastassios:    interested in knowing the status of big.LITTLE support in Xen
Dario:          went through the thread on the ML. The consensus seems to be
                based on vcpu pin/affinity.
Anastassios:    There are issue the way xen handles boot code. Wrong errata
                for cpus.
Julien:         Core could have different errata and features. Errata already
                works today.
                We need a summary of the discussion.

Dario stepped in to write a summary.

Anastassios:    What is the best board to work big.LITTLE with Xen?

?:              Renesas

ACTION: Dario to write a summary of the big.LITTLE discussions.

=== Secure Call Monitor (SMC) from guests ===

Andrii/Artem:   EPAM is working on allowing a guest to make call to TEE (e.g
                OPTEE). They are working in collaboration with Linaro to
                make OPTEE  virtualization aware. A design document has been
                posted on the ML (see [3]).
Edgar:          interested on this. Trusted world need to be accessed to
                manage FPGA and for power management

=== Running unmodified baremetal software in a guest ===

Edgar:          Xilinx is working on running unmodified baremetal software
                in a guest. Piece of work required:
                    - Mapping memory area with different memory attribut
                      to domU
                    - Replicate host memory map
                    - Exposing a vUART to guest (see [4] for the discussion)
Steward:        vUART is very important, especially for baremetal guests
Stefano:        it would need to be loggable
Julien:         we would have the same issue in the future to be compliant
                with the VM Spec (see [5]).

=== Areas of concern ===

Bosch: problem with xen-swiotlb. It does not work properly on renesas board.
Stefano: please report the error on the ML

ACTION: Bosch to send a bug report regarding xen-swiotlb

Edgar:  IOMMU could not be used by the guest (Stage-1). This would be useful
        to implement driver in userspace.
Julien: When will it be required?
Edgar:  It is a trend

Julien: Should we organized another Community Call? When?
Artem: Once per month is a good start

All: Agreed on a call before Christmas

[1] https://lists.xenproject.org/archives/html/xen-devel/2016-10/msg01966.html
[2] https://lists.xenproject.org/archives/html/xen-devel/2016-09/msg01802.html
[3] https://lists.xenproject.org/archives/html/xen-devel/2016-11/msg02220.html
[4] https://lists.xenproject.org/archives/html/xen-devel/2016-11/msg00846.html
[5] 
http://people.linaro.org/~christoffer.dall/VMSystemSpecificationForARM-v2.0.pdf

-- 
Julien Grall

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