[Xen-devel] soft reset support on Arm (Was: Re: 回复：回复：Re: Xen ARM Fault recovery for automotive use case)

[Julien Grall <julien.grall@xxxxxxx>]

(+ Stefano, Wei and Ian)

Hello,

Apologies for the late answer.

First of all, please avoid sending e-mail using HTML encoding. E-mail on 
mailing should only be plain text.
On 3/20/19 9:28 AM, ramblech@xxxxxxxx wrote:
>  > On 18/03/2019 06:50, ramblech@xxxxxxxx wrote:
>  > > Hello,
>  > Hello,
>  > > I'm researching xen for automotive use case and I see a 
> presentation called:
>  > > "Design and Implementation of Automotive Virtualization Based on 
> Xen - Sung-Min
>  > > Lee, Samsung Electronics"
>  > > on Xen Developer and Design Summit 2018.
>  > >
>  > > I'm interesting in the modification of fault recovery scenario on 
> P9~P11, it
>  > > introduced a new hypercall called XEN_DOMCTL_samsung_reset.
>  > If I recall correctly the talk, XEN_DOMCTL_samsung_reset is doing 
> exactly the
>  > same as XEN_DOMCTL_soft_reset. The later is not yet implemented on 
> Arm, I can
>  > provide guidelines if you are interested to implement it.
>
> Thank you for your reply!
> It will be very useful if there is some guide for implement the soft_reset.
(See below).

> And are there any plan for official implementation of this function on ARM?
I am not aware of anyone working on the implementation for Arm. I would 
be happy to review any patch series sent.
>  > Where can I find some code or tutorial for this modification? Has the 
> code been
>  > released?
>  > Your best bet would be to contact the speaker.
>  > Best regards,
>  > --
>  > Julien Grall
>
> I check the code in xl, in function libxl_domain_soft_reset there is a 
> check that
> if (info->type != LIBXL_DOMAIN_TYPE_HVM) return ERROR_INVAL;
>
> So the ARM use PVH type can't use this function.
AFAICT, this is HVM only because the softreset code relies on the 
presence of a device-model. PVH guest does not have a device model, the 
code at the end of the function do_domain_soft_reset would need to be 
adapted to remove any reference on the device model.
> Are there any guide or sample code for implementation of this feature?
I haven't fully though about the soft reset on Arm.

From my understanding, for a first implementation, replacing the domain 
shared info page with a new page (see the implementation in the x86 
version of arch_domain_create) should be sufficient. You should be able 
to soft_reset your domain afterwards.
For a more robust implementation, I think we need to warn if foreign 
mappings are still present because they are mapping to another guest. 
There might be interesting thing happening if they are still present. 
You would need to go through the P2M and check if there are a foreign 
mappings in place.
There might be other mappings to take care of (i.e grant-table...) but I 
didn't have time to look whether it is strictly necessary yet.
I have CCed some person that should be able to give feedback on libxl 
and complete if I miss anything.
Cheers,


--
Julien Grall

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