linux-kernel - Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid

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Date:   Tue, 10 May 2022 12:23:30 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 08/12] iommu/sva: Use attach/detach_pasid_dev in SVA
 interfaces

On Tue, May 10, 2022 at 02:17:34PM +0800, Lu Baolu wrote:

> +/**
> + * iommu_sva_bind_device() - Bind a process address space to a device
> + * @dev: the device
> + * @mm: the mm to bind, caller must hold a reference to mm_users
> + * @drvdata: opaque data pointer to pass to bind callback
> + *
> + * Create a bond between device and address space, allowing the device to access
> + * the mm using the returned PASID. If a bond already exists between @device and
> + * @mm, it is returned and an additional reference is taken. Caller must call
> + * iommu_sva_unbind_device() to release each reference.
> + *
> + * iommu_dev_enable_feature(dev, IOMMU_DEV_FEAT_SVA) must be called first, to
> + * initialize the required SVA features.
> + *
> + * On error, returns an ERR_PTR value.
> + */
> +struct iommu_sva *
> +iommu_sva_bind_device(struct device *dev, struct mm_struct *mm, void *drvdata)
> +{
> +	int ret = -EINVAL;
> +	struct iommu_sva *handle;
> +	struct iommu_domain *domain;
> +
> +	/*
> +	 * TODO: Remove the drvdata parameter after kernel PASID support is
> +	 * enabled for the idxd driver.
> +	 */
> +	if (drvdata)
> +		return ERR_PTR(-EOPNOTSUPP);

Why is this being left behind? Clean up the callers too please.

> +	/* Allocate mm->pasid if necessary. */
> +	ret = iommu_sva_alloc_pasid(mm, 1, (1U << dev->iommu->pasid_bits) - 1);
> +	if (ret)
> +		return ERR_PTR(ret);
> +
> +	mutex_lock(&iommu_sva_lock);
> +	/* Search for an existing bond. */
> +	handle = xa_load(&dev->iommu->sva_bonds, mm->pasid);
> +	if (handle) {
> +		refcount_inc(&handle->users);
> +		goto out_success;
> +	}

How can there be an existing bond?

dev->iommu is per-device

The device_group_immutable_singleton() insists on a single device
group

Basically 'sva_bonds' is the same thing as the group->pasid_array.

Assuming we leave room for multi-device groups this logic should just
be

	group = iommu_group_get(dev);
	if (!group)
		return -ENODEV;

	mutex_lock(&group->mutex);
	domain = xa_load(&group->pasid_array, mm->pasid);
	if (!domain || domain->type != IOMMU_DOMAIN_SVA || domain->mm != mm)
		domain = iommu_sva_alloc_domain(dev, mm);

?

And stick the refcount in the sva_domain

Also, given the current arrangement it might make sense to have a
struct iommu_domain_sva given that no driver is wrappering this in
something else.

Jason