[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [PATCH] xen: arm: Spin-up cpu instead PSCI CPU OFF



Hi Dmytro,

Title: It seems to suggest we are completely removing PSCI CPU off. I would suggest to rename to:

xen/arm: Don't use stop_cpu() in halt_this_cpu()

On 22/06/2022 08:24, dmitry.semenets@xxxxxxxxx wrote:
From: Dmytro Semenets <dmytro_semenets@xxxxxxxx>

Use spin-up cpu with disabled interrupts instead PSCI CPU OFF
halt and reboot procedures. Some platforms can't stop CPU via PSCI
because Thrusted OS can't migrate execution to other CPU.

There are some information missing:
 - What's the problem if we don't do that (i.e. Xen will panic())
 - Reference to the spec
 - Why this is fine to not use PSCI off

I would suggest the following commit message:

"
When shutting down (or rebooting) the platform, Xen will call stop_cpu() on all the CPUs but one. The last CPU will then request the system to shutdown/restart.

On platform using PSCI, stop_cpu() will call PSCI CPU off. Per the spec (section 5.5.2 DEN0022D.b), the call could return DENIED if the Trusted OS is resident on the CPU that is about to be turned off.

As Xen doesn't migrate off the trusted OS (which BTW may not be migratable), it would be possible to hit the panic().

In the ideal situation, Xen should migrate the trusted OS or make sure the CPU off is not called. However, when shutting down (or rebooting) the platform, it is pointless to try to turn off all the CPUs (per section 5.10.2, it is only required to put the core in a known state).

So solve the problem by open-coding stop_cpu() in halt_this_cpu() and not call PSCI CPU off.
"

I will give an opportunity for you, Bertrand and Stefano to answer before committing it.

Cheers,

--
Julien Grall



 


Rackspace

Lists.xenproject.org is hosted with RackSpace, monitoring our
servers 24x7x365 and backed by RackSpace's Fanatical Support®.