linux-kernel - Re: [PATCH v5 2/8] iommu/vt-d: Add per-device IOMMU feature ops entries

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Date:   Fri, 11 Jan 2019 12:16:44 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>, ashok.raj@...el.com,
        sanjay.k.kumar@...el.com, jacob.jun.pan@...el.com,
        kevin.tian@...el.com,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        yi.l.liu@...el.com, yi.y.sun@...el.com, peterx@...hat.com,
        tiwei.bie@...el.com, Zeng@...tes.org, Xin <xin.zeng@...el.com>,
        iommu@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [PATCH v5 2/8] iommu/vt-d: Add per-device IOMMU feature ops
 entries

Hi,

this looks a bit confusing to me because I can see no checking whether
the device actually supports scalable mode. More below:

On Thu, Jan 10, 2019 at 11:00:21AM +0800, Lu Baolu wrote:
> +static int intel_iommu_enable_auxd(struct device *dev)
> +{
> +	struct device_domain_info *info;
> +	struct dmar_domain *domain;
> +	unsigned long flags;
> +
> +	if (!scalable_mode_support())
> +		return -ENODEV;
> +
> +	domain = get_valid_domain_for_dev(dev);
> +	if (!domain)
> +		return -ENODEV;
> +
> +	spin_lock_irqsave(&device_domain_lock, flags);
> +	info = dev->archdata.iommu;
> +	info->auxd_enabled = 1;
> +	spin_unlock_irqrestore(&device_domain_lock, flags);
> +
> +	return 0;
> +}

This code sets a flag to mark scalable mode enabled. Doesn't the device
need some handling too, like enabling the PASID capability and all?

> +
> +static bool
> +intel_iommu_dev_has_feat(struct device *dev, enum iommu_dev_features feat)
> +{
> +	struct device_domain_info *info = dev->archdata.iommu;
> +
> +	if (feat == IOMMU_DEV_FEAT_AUX)
> +		return scalable_mode_support() && info && info->auxd_enabled;
> +
> +	return false;
> +}

Why is this checking the auxd_enabled flag? The function should just
return whether the device _supports_ scalable mode, not whether it is
enabled.

Regards,

	Joerg