linux-kernel - Re: [PATCH RFC 06/11] iommu/sva: Use attach/detach_pasid

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Message-ID: <YjhiohZAbN1ornmB@myrica>
Date:   Mon, 21 Mar 2022 11:33:54 +0000
From:   Jean-Philippe Brucker <jean-philippe@...aro.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>, Jason Gunthorpe <jgg@...dia.com>,
        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>,
        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 RFC 06/11] iommu/sva: Use attach/detach_pasid_dev in SVA
 interfaces

On Sun, Mar 20, 2022 at 02:40:25PM +0800, Lu Baolu wrote:
> diff --git a/drivers/iommu/iommu-sva-lib.c b/drivers/iommu/iommu-sva-lib.c
> index 106506143896..47cf98e661ff 100644
> --- a/drivers/iommu/iommu-sva-lib.c
> +++ b/drivers/iommu/iommu-sva-lib.c
> @@ -3,6 +3,8 @@
>   * Helpers for IOMMU drivers implementing SVA
>   */
>  #include <linux/mutex.h>
> +#include <linux/iommu.h>
> +#include <linux/slab.h>
>  #include <linux/sched/mm.h>
>  
>  #include "iommu-sva-lib.h"
> @@ -69,3 +71,101 @@ struct mm_struct *iommu_sva_find(ioasid_t pasid)
>  	return ioasid_find(&iommu_sva_pasid, pasid, __mmget_not_zero);
>  }
>  EXPORT_SYMBOL_GPL(iommu_sva_find);
> +
> +static struct iommu_domain *iommu_sva_domain_alloc(struct device *dev)
> +{
> +	struct bus_type *bus = dev->bus;
> +	struct iommu_domain *domain;
> +
> +	if (!bus || !bus->iommu_ops)
> +		return NULL;
> +
> +	domain = bus->iommu_ops->domain_alloc(IOMMU_DOMAIN_SVA);
> +	if (domain)
> +		domain->type = IOMMU_DOMAIN_SVA;
> +
> +	return domain;
> +}
> +
> +/**
> + * 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 it
> + * @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.

This is not true anymore, we return a different structure for each call.

> 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;
> +
> +	handle = kzalloc(sizeof(*handle), GFP_KERNEL);
> +	if (!handle)
> +		return ERR_PTR(-ENOMEM);
> +
> +	ret = iommu_sva_alloc_pasid(mm, 1, (1U << dev->iommu->pasid_bits) - 1);
> +	if (ret)
> +		goto out;
> +
> +	domain = iommu_sva_domain_alloc(dev);
> +	if (!domain) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +	domain->sva_cookie = mm;
> +
> +	ret = iommu_attach_device_pasid(domain, dev, mm->pasid);
> +	if (ret)
> +		goto out_free_domain;
> +
> +	handle->dev = dev;
> +	handle->domain = domain;
> +	handle->pasid = mm->pasid;
> +
> +	return handle;
> +
> +out_free_domain:
> +	iommu_domain_free(domain);
> +out:
> +	kfree(handle);
> +
> +	return ERR_PTR(ret);
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_bind_device);
> +
> +/**
> + * iommu_sva_unbind_device() - Remove a bond created with iommu_sva_bind_device
> + * @handle: the handle returned by iommu_sva_bind_device()
> + *
> + * Put reference to a bond between device and address space.

Same here. But I'd prefer keeping the old behavior so device drivers don't
have to keep track of {dev, mm} pairs themselves.

Thanks,
Jean

> The device should
> + * not be issuing any more transaction for this PASID. All outstanding page
> + * requests for this PASID must have been flushed to the IOMMU.
> + */
> +void iommu_sva_unbind_device(struct iommu_sva *handle)
> +{
> +	struct device *dev = handle->dev;
> +	struct iommu_domain *domain = handle->domain;
> +	struct mm_struct *mm = domain->sva_cookie;
> +
> +	iommu_detach_device_pasid(domain, dev, mm->pasid);
> +	iommu_domain_free(domain);
> +	kfree(handle);
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_unbind_device);
> +
> +u32 iommu_sva_get_pasid(struct iommu_sva *handle)
> +{
> +	return handle->pasid;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_get_pasid);