Re: [Xen-devel] [PATCH 05/18] xen/arm: Trigger Xen suspend when Dom0 completes suspend

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

On 12/11/2018 23:46, Stefano Stabellini wrote:
> On Mon, 12 Nov 2018, Julien Grall wrote:
> > Hi,
> >
> > On 11/12/18 11:30 AM, Mirela Simonovic wrote:
> > > When Dom0 finalizes its suspend procedure the suspend of Xen is
> > > triggered by calling system_suspend(). Dom0 finalizes the suspend from
> > > its boot core (VCPU#0), which could be mapped to any physical CPU,
> > > i.e. the system_suspend() function could be executed by any physical
> > > CPU. Since Xen suspend procedure has to be run by the boot CPU
> > > (non-boot CPUs will be disabled at some point in suspend procedure),
> > > system_suspend() execution has to continue on CPU#0.
> > Nothing in the domain_suspend code checks that domain_suspend is called by
> > vCPU0. I also can't find any restriction in the PSCI spec to run on pCPU0. Can
> > you provide more details why this required?
> The spec says that "to use this API, a calling OS must power down all
> but one core through calls to CPU_OFF". It is natural to think that the
> remaining core would be (physical or virtual) cpu0, but actually it is
> not clearly stated by the spec. For dom0, we could simply check that
> only 1 vcpu is left ON.
It is what we already do in the code. The comment and commit message does not 
match the code.
> For Xen and the physical system_suspend call,
> it makes sense to make the call on pcpu0.
This needs some rationale. What's wrong with issue the suspend from the current 
pCPU?
Cheers,

--
Julien Grall

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