linux-kernel - Re: [RFC PATCH v2 08/10] vfio/type1: Add domain at(de)taching group helpers

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Date:   Wed, 12 Sep 2018 13:02:00 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kirti Wankhede <kwankhede@...dia.com>
Cc:     baolu.lu@...ux.intel.com, kevin.tian@...el.com,
        ashok.raj@...el.com, tiwei.bie@...el.com, sanjay.k.kumar@...el.com,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        yi.y.sun@...el.com, jacob.jun.pan@...el.com, kvm@...r.kernel.org
Subject: Re: [RFC PATCH v2 08/10] vfio/type1: Add domain at(de)taching group
 helpers

Hi,

On 09/11/2018 12:23 AM, Jean-Philippe Brucker wrote:
> On 30/08/2018 05:09, Lu Baolu wrote:
>> +static int vfio_detach_aux_domain(struct device *dev, void *data)
>> +{
>> +	struct iommu_domain *domain = data;
>> +
>> +	vfio_mdev_set_aux_domain(dev, NULL);
>> +	iommu_detach_device(domain, dev->parent);
> 
> I think that's only going to work for vt-d, which doesn't use a
> default_domain. For other drivers, iommu.c ends up calling
> domain->ops->attach_dev(default_domain, dev) here, which isn't what we want.

This doesn't break any functionality. It takes effect only if iommu
hardware supports finer granular translation and advertises it through
the API.

> 
> That was my concern with reusing attach/detach_dev callbacks for PASID
> management. The attach_dev code of IOMMU drivers already has to deal
> with toggling between default and unmanaged domain. Dealing with more
> state transitions in the same path is going to be difficult.

Let's consider it from the API point of view.

We have iommu_a(de)ttach_device() APIs to attach or detach a domain
to/from a device. We should avoid applying a limitation of "these are
only for single domain case, for multiple domains, use another API".

Best regards,
Lu Baolu