Re: [RFC PATCH v2 31/35] arm64: psci: Ignore DENIED CPUs

[Gavin Shan]

On 9/15/23 02:01, Jonathan Cameron wrote:
> On Wed, 13 Sep 2023 16:38:19 +0000
> James Morse <james.morse@xxxxxxx> wrote:
>
> > From: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> >
> > When a CPU is marked as disabled, but online capable in the MADT, PSCI
> > applies some firmware policy to control when it can be brought online.
> > PSCI returns DENIED to a CPU_ON request if this is not currently
> > permitted. The OS can learn the current policy from the _STA enabled bit.
> >
> > Handle the PSCI DENIED return code gracefully instead of printing an
> > error.
>
> Specification reference would be good particularly as it's only been
> added as a possibility fairly recently.

https://developer.arm.com/documentation/den0022/f/?lang=en   page-58

It seems DENIED is the best matched indicator.

> > Signed-off-by: Jean-Philippe Brucker <jean-philippe@xxxxxxxxxx>
> > [ morse: Rewrote commit message ]
> > Signed-off-by: James Morse <james.morse@xxxxxxx>
> > ---
> >   arch/arm64/kernel/psci.c     | 2 +-
> >   arch/arm64/kernel/smp.c      | 3 ++-
> >   drivers/firmware/psci/psci.c | 2 ++
> >   3 files changed, 5 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm64/kernel/psci.c b/arch/arm64/kernel/psci.c
> > index 29a8e444db83..4fcc0cdd757b 100644
> > --- a/arch/arm64/kernel/psci.c
> > +++ b/arch/arm64/kernel/psci.c
> > @@ -40,7 +40,7 @@ static int cpu_psci_cpu_boot(unsigned int cpu)
> >   {
> >   	phys_addr_t pa_secondary_entry = __pa_symbol(secondary_entry);
> >   	int err = psci_ops.cpu_on(cpu_logical_map(cpu), pa_secondary_entry);
> > -	if (err)
> > +	if (err && err != -EPROBE_DEFER)
>
> Hmm. EPROBE_DEFER has very specific meaning around driver requesting a retry
> when some other bit of the system has finished booting.
> I'm not sure it's a good idea for this use case.  Maybe just keep to EPERM
> as psci_to_linux_errno() will return anyway.  Seems valid to me, or
> is the requirement to use EPROBE_DEFER coming from further up the stack?

I agree with Jonathan that -EPERM from psci_to_linux_errno(DENIED) is
good enough here. Actually, I think we need to bail from bringing up
the CPU once error is raised on psci_ops.cpu_on() and avoid reporting
it as error with help of -EPROBE_DEFER. -EPERM can serve the same
purpose.

> >   		pr_err("failed to boot CPU%d (%d)\n", cpu, err);
> >   
> >   	return err;
> > diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
> > index 8c8f55721786..e958db987665 100644
> > --- a/arch/arm64/kernel/smp.c
> > +++ b/arch/arm64/kernel/smp.c
> > @@ -124,7 +124,8 @@ int __cpu_up(unsigned int cpu, struct task_struct *idle)
> >   	/* Now bring the CPU into our world */
> >   	ret = boot_secondary(cpu, idle);
> >   	if (ret) {
> > -		pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
> > +		if (ret != -EPROBE_DEFER)
> > +			pr_err("CPU%u: failed to boot: %d\n", cpu, ret);
> >   		return ret;
> >   	}
> >   
> > diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> > index d9629ff87861..f7ab3fed3528 100644
> > --- a/drivers/firmware/psci/psci.c
> > +++ b/drivers/firmware/psci/psci.c
> > @@ -218,6 +218,8 @@ static int __psci_cpu_on(u32 fn, unsigned long cpuid, unsigned long entry_point)
> >   	int err;
> >   
> >   	err = invoke_psci_fn(fn, cpuid, entry_point, 0);
> > +	if (err == PSCI_RET_DENIED)
> > +		return -EPROBE_DEFER;
> >   	return psci_to_linux_errno(err);
> >   }
> >   

Thanks,
Gavin