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Re: [Xen-devel] [PATCH 17/18] xen/arm: Resume Dom0 after Xen resumes

On 16/11/2018 12:34, Mirela Simonovic wrote:
Hi Julien,

Hi Mirela,

On Fri, Nov 16, 2018 at 12:44 PM Julien Grall <julien.grall@xxxxxxx> wrote:

On 16/11/2018 11:29, Mirela Simonovic wrote:
On Fri, Nov 16, 2018 at 11:33 AM Mirela Simonovic
<mirela.simonovic@xxxxxxxxxx> wrote:

Hi Julien,

On Thu, Nov 15, 2018 at 9:31 PM Julien Grall <julien.grall@xxxxxxx> wrote:


On 11/12/18 11:30 AM, Mirela Simonovic wrote:
The resume of Dom0 should always follow Xen's resume. This is
done by unblocking the first vCPU of Dom0.

Please explain why you always need to resume Dom0 afterwards.

We don't need to, but that is what is promised in the design spec.

You surely had some rationale when writing the promise in the design document,

So what is the reason behind it? I don't want to resume a domain if that's not

To be more specific - a domU that doesn't depend on dom0 can resume
and work happily without dom0 being resumed, i.e. just Xen and domU
resume. So patch "[PATCH 17/18] xen/arm: Resume Dom0 after Xen
resumes" is not a must (when there are no PV drivers involved).

PV backends don't necessarily reside in the hardware domain. So how is this
going to work for the other case?

I honestly believe that this is not necessary, and is sub-optimal. It
relies on an assumption that dom0 contains all the PV drivers, which
is not always correct.

Well, there are other reasons to resume the hardware domain. The hardware domain owns most the devices and may be part of the suspend/resume path.

As you tie the host suspend to the hardware domain suspend, it may makes sense to resume at the same time. It is the kind of rationale I would expect in the commit message.

I would prefer if someone can tell us that any frontend will trigger
an event to the backend, and the event would go through Xen. That way,
this event would cause a domain containing the backend driver to
resume. I think this is the best possible solution, but it relies on
an assumption that the event will go through Xen, and I'm not
knowledgeable enough to claim that this is indeed the case.

I think it is should work, the best way to find out if building a test case for 


Julien Grall

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