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

Hi Stefano,

On 12/11/2018 23:46, Stefano Stabellini wrote:
On Mon, 12 Nov 2018, Julien Grall wrote:

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?


Julien Grall

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