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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Thu, Mar 21, 2019 at 06:20:42PM +0000, Julien Grall wrote:
> (+ 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.

Soft reset was created with HVM in mind so I wouldn't be surprised there
was a check for HVM guest type.

Now we have PVH guest type (for x86 and ARM), checking for device model
should definitely be conditional on HVM guest type, a knob in
configuration or guest runtime state.

> 
> > 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.

Going through x86 side patches would be a good start.

Wei.

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