linux-kernel - Re: [PATCH v6 10/29] iommu/vt-d: Implement minor tweaks for NMI irqs

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Message-ID: <20220513180744.GB22683@ranerica-svr.sc.intel.com>
Date:   Fri, 13 May 2022 11:07:44 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     x86@...nel.org, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Suravee Suthikulpanit <Suravee.Suthikulpanit@....com>,
        David Woodhouse <dwmw2@...radead.org>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Nicholas Piggin <npiggin@...il.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Ricardo Neri <ricardo.neri@...el.com>,
        iommu@...ts.linux-foundation.org, linuxppc-dev@...ts.ozlabs.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 10/29] iommu/vt-d: Implement minor tweaks for NMI irqs

On Fri, May 06, 2022 at 11:23:23PM +0200, Thomas Gleixner wrote:
> On Thu, May 05 2022 at 16:59, Ricardo Neri wrote:
> > The Intel IOMMU interrupt remapping driver already programs correctly the
> > delivery mode of individual irqs as per their irq_data. Improve handling
> > of NMIs. Allow only one irq per NMI. Also, it is not necessary to cleanup
> > irq vectors after updating affinity.
> 
> Structuring a changelog in paragraphs might make it readable. New lines
> exist for a reason.

Sure, I can structure this in paragraphps.
> 
> > NMIs do not have associated vectors.
> 
> Again. NMI has an vector associated, but it is not subject to dynamic
> vector management.

Indeed, it is clear to me now.

> 
> > diff --git a/drivers/iommu/intel/irq_remapping.c b/drivers/iommu/intel/irq_remapping.c
> > index fb2d71bea98d..791a9331e257 100644
> > --- a/drivers/iommu/intel/irq_remapping.c
> > +++ b/drivers/iommu/intel/irq_remapping.c
> > @@ -1198,8 +1198,12 @@ intel_ir_set_affinity(struct irq_data *data, const struct cpumask *mask,
> >  	 * After this point, all the interrupts will start arriving
> >  	 * at the new destination. So, time to cleanup the previous
> >  	 * vector allocation.
> > +	 *
> > +	 * Do it only for non-NMI irqs. NMIs don't have associated
> > +	 * vectors.
> 
> See above.

Sure.

> 
> >  	 */
> > -	send_cleanup_vector(cfg);
> > +	if (cfg->delivery_mode != APIC_DELIVERY_MODE_NMI)
> > +		send_cleanup_vector(cfg);
> 
> So this needs to be replicated for all invocations of
> send_cleanup_vector(), right? Why can't you put it into that function?

Certainly, it can be done inside the function.

>   
> >  	return IRQ_SET_MASK_OK_DONE;
> >  }
> > @@ -1352,6 +1356,9 @@ static int intel_irq_remapping_alloc(struct irq_domain *domain,
> >  	if (info->type == X86_IRQ_ALLOC_TYPE_PCI_MSI)
> >  		info->flags &= ~X86_IRQ_ALLOC_CONTIGUOUS_VECTORS;
> >  
> > +	if ((info->flags & X86_IRQ_ALLOC_AS_NMI) && nr_irqs != 1)
> > +		return -EINVAL;
> 
> This cannot be reached when the vector allocation domain already
> rejected it, but copy & pasta is wonderful and increases the line count.

Yes, this is not needed.

Thanks and BR,
Ricardo
> 
> Thanks,
> 
>         tglx
> 
>