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

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Message-ID: <878rtl272y.wl-maz@kernel.org>
Date:   Mon, 07 Mar 2022 14:03:17 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     John Garry <john.garry@...wei.com>
Cc:     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>,
        David Decotigny <decot@...gle.com>
Subject: Re: PCI MSI issue for maxcpus=1

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

-- 
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