Re: [PATCH] irqchip/gic-v4.1: Disallow setting affinity for virtual SGIs

[Zenghui Yu]

Hi Marc,

On 2020/4/11 17:41, Marc Zyngier wrote:
> Hi Zenghui,
>
> On Sat, 11 Apr 2020 10:10:32 +0100,
> Zenghui Yu <yuzenghui@xxxxxxxxxx> wrote:
> > Running a guest on the GICv4.1-implemented board, we will get the
> > following warning:
> >
> > [   59.062120] genirq: irq_chip GICv4.1-sgi did not update eff. affinity mask of irq 46
> >
> > It may be caused by irqbalance (or other userspace tools) which tries to
> > change the affinity of virtual SGIs on the host. One way to "fix" it is
> > to update the effective_affinity value in irq_set_affinity callback. But
> > as the comment above says, "There is no notion of affinity for virtual
> > SGIs, at least not on the host", doing so only makes things confusing.
> >
> > Given the vSGIs are private to the specified vPE, changing the affinity
> > on host is actually meaningless and achieves nothing. Let's just forbid
> > it.
> >
> > Reported-by: Nianyao Tang <tangnianyao@xxxxxxxxxx>
> > Signed-off-by: Zenghui Yu <yuzenghui@xxxxxxxxxx>
> > ---
> >
> > Hi Marc,
> >
> > This just restores the behavior of your v5 [*]. I wonder that what's the
> > reason to change it to 'return IRQ_SET_MASK_OK' in v6? What I've missed
> > here?
> >
> > [*] https://lore.kernel.org/kvm/20200304203330.4967-9-maz@xxxxxxxxxx/
>
> Not allowing the affinity move results in the kernel screaming when
> playing with CPU hotplug (it really wants to move the interrupt
> around). Which is why I dropped the -EINVAL, therefore introducing
> another bug. I fixed it with this patch[1], which I was planning to
> post after -rc1.

I didn't realize the CPU hotplug case. Please take your approach to
fix it. (As mentioned, this was also one way I planned to fix it.)

> Let me know what you think

TBH, I'm not very familiar with the IRQ core behavior on CPU hotplug.
I will read further and comment on your formal patch (please cc me),
but now spinning on some other things...


Thanks,
Zenghui