Re: [PATCH] riscv: Add initial Xen guest support for RISC-V

[Milan Đokić]

Hello Stefano, Oleksii

On Wed, Jan 15, 2025 at 5:30 PM Oleksii Kurochko
<oleksii.kurochko@xxxxxxxxx> wrote:
>
> Hi Stefano,
>
> On 1/15/25 1:01 AM, Stefano Stabellini wrote:
>
> +Oleksii
>
> On Tue, 14 Jan 2025, Milan Djokic wrote:
>
> From: Slavisa Petrovic <Slavisa.Petrovic@xxxxxxxxx>
>
> This patch introduces initial support for running RISC-V as a Xen guest.
> It provides the necessary infrastructure and stubs for Xen-specific
> operations. Key changes include:
>
> - Modifications to the RISC-V kernel to integrate Xen-specific hypercalls
>   and interfaces, with function implementations stubbed for future work.
> - Introduction of Xen-specific headers for RISC-V, including event
>   handling, hypervisor interaction, and page management. Functions are
>   defined but not yet implemented.
> - Stub implementations for memory management, grant tables, and context
>   switching in the Xen environment, allowing further development and
>   integration.
>
> Signed-off-by: Milan Djokic <Milan.Djokic@xxxxxxxxx>
> Signed-off-by: Slavisa Petrovic <Slavisa.Petrovic@xxxxxxxxx>
>
> Hi Milan, Slavisa,
>
> Thank you very much for your contribution! Which Xen tree are you using
> for development?
>
> They are using [1] and have separate branches on top of latest. So we are in
> sync. Also, if you are interested we have created a task/epics for this feature in
> [1] so you could also check there some details:
> 1. https://gitlab.com/groups/xen-project/people/olkur/-/epics/5
> 2. https://gitlab.com/xen-project/people/olkur/xen/-/issues/12
>
>  I am asking because RISC-V support in Xen is still in
> the process of being upstreamed, and [1] is the tree that consolidates
> all patches currently on the to-be-upstreamed list.
>
> While the specific Xen tree you are using is not particularly important
> at this stage, and using [1] is not a requirement, I am asking because
> it is essential to align on the hypervisor ABI, especially regarding any
> details that have not yet been upstreamed. Specifically, is there
> anything in this patch series that relies on features not yet upstream
> in Xen?
>
> There are few features but some things which are Rt-Tk's branch in [1] could go
> without waiting for these features to be upstreamed.
>
> Thanks.
>
> ~ Oleksii
>
> [1] https://gitlab.com/xen-project/people/olkur/xen/-/tree/latest?ref_type=heads

As Oleksii already explained, we are working in sync with his latest
branch where most of the risc port is done.
I would just add that this patch introduces kernel risc-v hypercall
support on which only our branch on xen tree depends on. Therefore, it
won't disrupt any functionality with current upstream Xen, it will
just introduce kernel functionality which is not used from Xen side
until our branch is merged upstream.

Best regards,
Milan