Re: [Xen-devel] [PATCH v2 0/6] xen: simplify suspend/resume handling

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 3/28/19 1:56 PM, Volodymyr Babchuk wrote:
> On Thu, 28 Mar 2019 at 15:33, Julien Grall <julien.grall@xxxxxxx> wrote:
> > On 3/28/19 1:01 PM, Volodymyr Babchuk wrote:
> > > On Thu, 28 Mar 2019 at 14:09, Juergen Gross <jgross@xxxxxxxx> wrote:
> > > (XEN) ****************************************
> > > (XEN) Panic on CPU 0:
> > > (XEN) PSCI cpu off failed for CPU0 err=-3
> > > (XEN) ****************************************
> > PSCI CPU off failing is never a good news. Here, the command has been
> > denied by PSCI monitor. But... why does CPU off is actually called on
> > CPU0? Shouldn't we have turned off the platform instead?
> I think, this is because CPU1 is performing machine_restart(), so it
> asked CPU0 to halt itself.
The PSCI call SYSTEM_OFF/SYSTEM_RESET requires all the CPUs to be in a 
known state. The PSCI spec actually suggest to turn all the CPUs but one 
off. Another alternative is to put them in a quiescent state.
CPU_OFF will return -3 (i.e DENIED) if the Trusted OS is Uniprocessor 
and resides on the core that you are about to turn off. I assume your 
platform have a TOS UP and currently resides on CPU0.
SYSTEM_OFF/SYSTEM_RESET call can be done from any CPUs. If we want to 
avoid the problem with CPU_OFF, then the best options is to put the all 
CPUs but one in a quiescent state (something like while (1) cpu_relax/wfi).
On a side node, we should probably want to remove the panic in 
call_psci_cpu_off as this will be used by the suspend code. Indeed, the 
trusted OS may not reside on the boot CPU, so you may hit the panic as well.
> > > (XEN)
> > > (XEN) Reboot in five seconds...
> > Are the logs below actually a mistaken paste?
> No, this is what I'm seeing in my serial console.
I guess this is happening because we recurse in machine_halt(). We 
probably want to drop any panic in that code path.
Cheers,

--
Julien Grall

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