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

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Date:   Fri, 06 May 2022 23:23:23 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>,
        x86@...nel.org
Cc:     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,
        Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
Subject: Re: [PATCH v6 10/29] iommu/vt-d: Implement minor tweaks for NMI irqs

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.

> NMIs do not have associated vectors.

Again. NMI has an vector associated, but it is not subject to dynamic
vector management.

> 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.

>  	 */
> -	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?
  
>  	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.

Thanks,

        tglx