linux-kernel - Re: PCI MSI issue for maxcpus=1

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Message-ID: <CAG88wWYPxxi6m6B1gxyaPYbeQV3psK7QM1CnXN-E1P7_hRNTUA@mail.gmail.com>
Date:   Mon, 7 Mar 2022 17:37:23 -0800
From:   David Decotigny <ddecotig@...gle.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     John Garry <john.garry@...wei.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        chenxiang <chenxiang66@...ilicon.com>,
        Shameer Kolothum <shameerali.kolothum.thodi@...wei.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "liuqi (BA)" <liuqi115@...wei.com>, wangxiongfeng2@...wei.com
Subject: Re: PCI MSI issue for maxcpus=1

Thanks, Marc! That solved the issue on our end as well.

On Mon, Mar 7, 2022 at 6:03 AM Marc Zyngier <maz@...nel.org> wrote:
>
> On Mon, 07 Mar 2022 14:01:02 +0000,
> Marc Zyngier <maz@...nel.org> wrote:
> >
> > Hi John,
> >
> > On Mon, 07 Mar 2022 13:48:11 +0000,
> > John Garry <john.garry@...wei.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.
>
> [1] https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/log/?h=irq/msi-shutdown-on-init
>
> --
> Without deviation from the norm, progress is not possible.