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Subject: Re: [PATCH v3 03/16] iommu: Add I/O ASID allocator
To:     Jacob Pan <jacob.jun.pan@linux.intel.com>,
        iommu@lists.linux-foundation.org,
        LKML <linux-kernel@vger.kernel.org>,
        Joerg Roedel <joro@8bytes.org>,
        David Woodhouse <dwmw2@infradead.org>,
        Alex Williamson <alex.williamson@redhat.com>,
        Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Cc:     Yi Liu <yi.l.liu@intel.com>, "Tian, Kevin" <kevin.tian@intel.com>,
        Raj Ashok <ashok.raj@intel.com>,
        Christoph Hellwig <hch@infradead.org>,
        Lu Baolu <baolu.lu@linux.intel.com>,
        Andriy Shevchenko <andriy.shevchenko@linux.intel.com>
References: <1556922737-76313-1-git-send-email-jacob.jun.pan@linux.intel.com>
 <1556922737-76313-4-git-send-email-jacob.jun.pan@linux.intel.com>
From:   Auger Eric <eric.auger@redhat.com>
Message-ID: <bb31fbcb-2708-93e6-f11e-3018556fbc21@redhat.com>
Date:   Tue, 21 May 2019 10:21:55 +0200
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Hi,

On 5/4/19 12:32 AM, Jacob Pan wrote:
> From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> 
> Some devices might support multiple DMA address spaces, in particular
> those that have the PCI PASID feature. PASID (Process Address Space ID)
> allows to share process address spaces with devices (SVA), partition a
> device into VM-assignable entities (VFIO mdev) or simply provide
> multiple DMA address space to kernel drivers. Add a global PASID
> allocator usable by different drivers at the same time. Name it I/O ASID
> to avoid confusion with ASIDs allocated by arch code, which are usually
> a separate ID space.
> 
> The IOASID space is global. Each device can have its own PASID space,
> but by convention the IOMMU ended up having a global PASID space, so
> that with SVA, each mm_struct is associated to a single PASID.
> 
> The allocator is primarily used by IOMMU subsystem but in rare occasions
> drivers would like to allocate PASIDs for devices that aren't managed by
> an IOMMU, using the same ID space as IOMMU.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Link: https://lkml.org/lkml/2019/4/26/462
> ---
>  drivers/iommu/Kconfig  |   6 +++
>  drivers/iommu/Makefile |   1 +
>  drivers/iommu/ioasid.c | 140 +++++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/ioasid.h |  67 +++++++++++++++++++++++
>  4 files changed, 214 insertions(+)
>  create mode 100644 drivers/iommu/ioasid.c
>  create mode 100644 include/linux/ioasid.h
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 6f07f3b..75e7f97 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -2,6 +2,12 @@
>  config IOMMU_IOVA
>  	tristate
>  
> +config IOASID
> +	bool
don't we want a tristate here too?

Also refering to the past discussions we could add "# The IOASID library
may also be used by non-IOMMU_API users"
> +	help
> +	  Enable the I/O Address Space ID allocator. A single ID space shared
> +	  between different users.
> +
>  # IOMMU_API always gets selected by whoever wants it.
>  config IOMMU_API
>  	bool
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 8c71a15..0efac6f 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -7,6 +7,7 @@ obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE) += io-pgtable.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_ARMV7S) += io-pgtable-arm-v7s.o
>  obj-$(CONFIG_IOMMU_IO_PGTABLE_LPAE) += io-pgtable-arm.o
> +obj-$(CONFIG_IOASID) += ioasid.o
>  obj-$(CONFIG_IOMMU_IOVA) += iova.o
>  obj-$(CONFIG_OF_IOMMU)	+= of_iommu.o
>  obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
> diff --git a/drivers/iommu/ioasid.c b/drivers/iommu/ioasid.c
> new file mode 100644
> index 0000000..99f5e0a
> --- /dev/null
> +++ b/drivers/iommu/ioasid.c
> @@ -0,0 +1,140 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * I/O Address Space ID allocator. There is one global IOASID space, split into
> + * subsets. Users create a subset with DECLARE_IOASID_SET, then allocate and
> + * free IOASIDs with ioasid_alloc and ioasid_free.
> + */
> +#include <linux/xarray.h>
> +#include <linux/ioasid.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +
> +struct ioasid_data {
> +	ioasid_t id;
> +	struct ioasid_set *set;
> +	void *private;
> +	struct rcu_head rcu;
> +};
> +
> +static DEFINE_XARRAY_ALLOC(ioasid_xa);
> +
> +/**
> + * ioasid_set_data - Set private data for an allocated ioasid
> + * @ioasid: the ID to set data
> + * @data:   the private data
> + *
> + * For IOASID that is already allocated, private data can be set
> + * via this API. Future lookup can be done via ioasid_find.
> + */
> +int ioasid_set_data(ioasid_t ioasid, void *data)
> +{
> +	struct ioasid_data *ioasid_data;
> +	int ret = 0;
> +
> +	ioasid_data = xa_load(&ioasid_xa, ioasid);
> +	if (ioasid_data)
> +		ioasid_data->private = data;
> +	else
> +		ret = -ENOENT;
> +
> +	/* getter may use the private data */
> +	synchronize_rcu();
> +
> +	return ret;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_set_data);
> +
> +/**
> + * ioasid_alloc - Allocate an IOASID
> + * @set: the IOASID set
> + * @min: the minimum ID (inclusive)
> + * @max: the maximum ID (inclusive)
> + * @private: data private to the caller
> + *
> + * Allocate an ID between @min and @max (or %0 and %INT_MAX).
I think we agreed to drop (or %0 and %INT_MAX)
 Return the
> + * allocated ID on success, or INVALID_IOASID on failure. The @private pointer
> + * is stored internally and can be retrieved with ioasid_find().
> + */
> +ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
> +		      void *private)
> +{
> +	int id = INVALID_IOASID;
isn't it an unsigned?
> +	struct ioasid_data *data;
> +
> +	data = kzalloc(sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return INVALID_IOASID;
> +
> +	data->set = set;
> +	data->private = private;
> +
> +	if (xa_alloc(&ioasid_xa, &id, data, XA_LIMIT(min, max), GFP_KERNEL)) {
> +		pr_err("Failed to alloc ioasid from %d to %d\n", min, max);
> +		goto exit_free;
> +	}
> +	data->id = id;
> +
> +exit_free:
> +	if (id < 0 || id == INVALID_IOASID) {
< 0?
> +		kfree(data);
> +		return INVALID_IOASID;
> +	}
> +	return id;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_alloc);
> +
> +/**
> + * ioasid_free - Free an IOASID
> + * @ioasid: the ID to remove
> + */
> +void ioasid_free(ioasid_t ioasid)
> +{
> +	struct ioasid_data *ioasid_data;
> +
> +	ioasid_data = xa_erase(&ioasid_xa, ioasid);
> +
> +	kfree_rcu(ioasid_data, rcu);
> +}
> +EXPORT_SYMBOL_GPL(ioasid_free);
> +
> +/**
> + * ioasid_find - Find IOASID data
> + * @set: the IOASID set
> + * @ioasid: the IOASID to find
> + * @getter: function to call on the found object
> + *
> + * The optional getter function allows to take a reference to the found object
> + * under the rcu lock. The function can also check if the object is still valid:
> + * if @getter returns false, then the object is invalid and NULL is returned.
> + *
> + * If the IOASID has been allocated for this set, return the private pointer
> + * passed to ioasid_alloc. Private data can be NULL if not set. Return an error
> + * if the IOASID is not found or not belong to the set.
do not belong
> + */
> +void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
> +		  bool (*getter)(void *))
> +{
> +	void *priv = NULL;
> +	struct ioasid_data *ioasid_data;
> +
> +	rcu_read_lock();
> +	ioasid_data = xa_load(&ioasid_xa, ioasid);
> +	if (!ioasid_data) {
> +		priv = ERR_PTR(-ENOENT);
> +		goto unlock;
> +	}
> +	if (set && ioasid_data->set != set) {
> +		/* data found but does not belong to the set */
> +		priv = ERR_PTR(-EACCES);
> +		goto unlock;
> +	}
> +	/* Now IOASID and its set is verified, we can return the private data */
> +	priv = ioasid_data->private;
> +	if (getter && !getter(priv))
> +		priv = NULL;
> +unlock:
> +	rcu_read_unlock();
> +
> +	return priv;
> +}
> +EXPORT_SYMBOL_GPL(ioasid_find);
> diff --git a/include/linux/ioasid.h b/include/linux/ioasid.h
> new file mode 100644
> index 0000000..41de5e4
> --- /dev/null
> +++ b/include/linux/ioasid.h
> @@ -0,0 +1,67 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __LINUX_IOASID_H
> +#define __LINUX_IOASID_H
> +
> +#define INVALID_IOASID ((ioasid_t)-1)
> +typedef unsigned int ioasid_t;
> +typedef int (*ioasid_iter_t)(ioasid_t ioasid, void *private, void *data);
> +typedef ioasid_t (*ioasid_alloc_fn_t)(ioasid_t min, ioasid_t max, void *data);
> +typedef void (*ioasid_free_fn_t)(ioasid_t ioasid, void *data);
> +
> +struct ioasid_set {
> +	int dummy;
> +};
> +
> +struct ioasid_allocator {
> +	ioasid_alloc_fn_t alloc;
> +	ioasid_free_fn_t free;
> +	void *pdata;
> +	struct list_head list;
> +};
> +
> +#define DECLARE_IOASID_SET(name) struct ioasid_set name = { 0 }
> +
> +#ifdef CONFIG_IOASID
> +ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min, ioasid_t max,
> +		      void *private);
> +void ioasid_free(ioasid_t ioasid);
> +
> +void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
> +		  bool (*getter)(void *));
> +int ioasid_register_allocator(struct ioasid_allocator *allocator);
> +void ioasid_unregister_allocator(struct ioasid_allocator *allocator);
> +
> +int ioasid_set_data(ioasid_t ioasid, void *data);
> +
> +#else /* !CONFIG_IOASID */
> +static inline ioasid_t ioasid_alloc(struct ioasid_set *set, ioasid_t min,
> +				    ioasid_t max, void *private)
> +{
> +	return INVALID_IOASID;
> +}
> +
> +static inline void ioasid_free(ioasid_t ioasid)
> +{
> +}
> +
> +static inline void *ioasid_find(struct ioasid_set *set, ioasid_t ioasid,
> +				bool (*getter)(void *))
> +{
> +	return NULL;
> +}
> +static inline int ioasid_register_allocator(struct ioasid_allocator *allocator)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline void ioasid_unregister_allocator(struct ioasid_allocator *allocator)
> +{
> +}
> +
> +static inline int ioasid_set_data(ioasid_t ioasid, void *data)
> +{
> +	return -ENODEV;
> +}
> +
> +#endif /* CONFIG_IOASID */
> +#endif /* __LINUX_IOASID_H */
> 
Thanks

Eric