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SubjectRe: PCI MSI issue for maxcpus=1
Hi John,

On Mon, 07 Mar 2022 13:48:11 +0000,
John Garry <john.garry@huawei.com> wrote:
>
> Hi Marc,
>
> >
> > diff --git a/kernel/irq/msi.c b/kernel/irq/msi.c
> > index 2bdfce5edafd..97e9eb9aecc6 100644
> > --- a/kernel/irq/msi.c
> > +++ b/kernel/irq/msi.c
> > @@ -823,6 +823,19 @@ static int msi_init_virq(struct irq_domain *domain, int virq, unsigned int vflag
> > if (!(vflags & VIRQ_ACTIVATE))
> > return 0;
> > + if (!(vflags & VIRQ_CAN_RESERVE)) {
> > + /*
> > + * If the interrupt is managed but no CPU is available
> > + * to service it, shut it down until better times.
> > + */
> > + if (irqd_affinity_is_managed(irqd) &&
> > + !cpumask_intersects(irq_data_get_affinity_mask(irqd),
> > + cpu_online_mask)) {
> > + irqd_set_managed_shutdown(irqd);
> > + return 0;
> > + }
> > + }
> > +
> > ret = irq_domain_activate_irq(irqd, vflags & VIRQ_CAN_RESERVE);
> > if (ret)
> > return ret;
> >
>
> Yeah, that seems to solve the issue. I will test it a bit more.

Thanks. For the record, I have pushed a branch at [1]. The patch is
extremely similar, just moved up a tiny bit to avoid duplicating the
!VIRQ_CAN_RESERVE case.

> We need to check the isolcpus cmdline issue as well - wang xiongfeng,
> please assist here. I assume that this feature just never worked for
> arm64 since it was added.

That one is still on my list. isolcpus certainly has had as little
testing as you can imagine.

> Out of interest, is the virtio managed interrupts support just in
> your sandbox? You did mention earlier in the thread that you were
> considering adding this feature.

As it turns out, QEMU's non-legacy virtio support allows the kernel to
do the right thing (multi-queue support and affinity management).
Using kvmtool, I only get a single interrupt although the device
pretends to support some MQ extension. I haven't dug into it yet.

M.
--
Without deviation from the norm, progress is not possible.

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