linux-kernel - Re: [PATCH v5 07/23] iommu/vt-d: fix dev iotlb pfsid use

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Date:   Mon, 14 May 2018 13:38:25 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Rafael Wysocki <rafael.j.wysocki@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Jean Delvare <khali@...ux-fr.org>,
        Christoph Hellwig <hch@...radead.org>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v5 07/23] iommu/vt-d: fix dev iotlb pfsid use

On Mon, 14 May 2018 09:52:04 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> > diff --git a/drivers/iommu/intel-iommu.c
> > b/drivers/iommu/intel-iommu.c index 4623294..732a10f 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -1459,6 +1459,19 @@ static void iommu_enable_dev_iotlb(struct
> > device_domain_info *info) return;
> >  
> >  	pdev = to_pci_dev(info->dev);
> > +	/* For IOMMU that supports device IOTLB throttling (DIT),
> > we assign
> > +	 * PFSID to the invalidation desc of a VF such that IOMMU
> > HW can gauge
> > +	 * queue depth at PF level. If DIT is not set, PFSID will
> > be treated as
> > +	 * reserved, which should be set to 0.
> > +	 */
> > +	if (!ecap_dit(info->iommu->ecap))
> > +		info->pfsid = 0;
> > +	else if (pdev && pdev->is_virtfn) {
> > +		if (ecap_(info->iommu->ecap))
> > +			dev_warn(&pdev->dev, "SRIOV VF device
> > IOTLB enabled without flow control\n");  
> 
> I can't understand these two lines.
> 
> Isn't the condition always true? What does the error message mean?

you are right, there is no need to check ecap_dit again. thanks!