Re: [RFC PATCH 1/5] iommu: Add APIs for IOMMU PASID management

[Jacob Pan]

On Mon, 12 Nov 2018 14:44:57 +0800
Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx> wrote:

> This adds APIs for IOMMU drivers and device drivers to manage
> the PASIDs used for DMA transfer and translation. It bases on
> I/O ASID allocator for PASID namespace management and relies
> on vendor specific IOMMU drivers for paravirtual PASIDs.
> 
Trying to integrate this with VT-d SVM code had some thoughts.
First of all, it seems to me the problem we are trying to solve here is
to allow custom PASID/IOASID allocator.
IOASID, as in driver base, is a common infrastructure of its own right.
So it is OK to let device drivers such as VT-d driver directly
communicate with IOASID w/o going through common IOMMU layer. Therefore
I see little value of adding this wrapper to ioasid code, instead I
feel it might be less work to enhance ioasid with the following:

1. allow ioasid code to register a system wide custom asid allocator,
which takes precedence over the idr allocator
e.g.
typedef ioasid_t (*ioasid_alloc_fn_t)(ioasid_t min, ioasid_t max, void *data);
void ioasid_set_allocator(ioasid_alloc_fn_t fn)
{}
We can still use idr for tracking ioasid and private data lookup, since
the ioasid idr is exclusively owned by ioasid_alloc, we can rest and be
sure there is no conflict with other callers. See code comments below.

2. support setting asid private data _after_ asid is allocated. The use
case is that PASID allocation and mm bind can be split into separate
stages. Private data (mm related) are not available at the time of
allocation, only bind time.
Since IDR needs the data pointer at allocation time, we can still
create an empty ioasid_data for ioasid tracking at alloc time. i.e.
struct ioasid_data {
	void *ptr; /* private data */
};


3. allow NULL ioasid_set
I also had a hard time understanding the use of ioasid_set, since there
is already a private data associated with each ioasid, is it not enough
to group ioasid based on private data?

So the usage scenarios can be.
1. during boot, vt-d driver register a custom ioasid allocator (vcmd) if
it detects its running as a guest.

2. Running as a guest, all pasid allocation via ioasid_alloc() will go
to this custom allocators and tracked

3. for native case, there is no custom allocator, ioasid just use IDR
alloc

4. for native bind mm, pasid allocation already has private data filled
in when calling ioasid_alloc

5. for guest bind, pasid is allocated with empty private data (called
by VFIO layer), but private data is filled in later by bind guest
pasid inside the vt-d driver.

So my thinking is that we can avoid having another layer of APIs as
below and keep everything within ioasid. Also allows private data to be
managed at lower level as compared to VFIO.


Thanks,

Jacob

> Below APIs are added:
> 
> * iommu_pasid_init(pasid)
>   - Initialize a PASID consumer. The vendor specific IOMMU
>     drivers are able to set the PASID range imposed by IOMMU
>     hardware through a callback in iommu_ops.
> 
> * iommu_pasid_exit(pasid)
>   - The PASID consumer stops consuming any PASID.
> 
> * iommu_pasid_alloc(pasid, min, max, private, *ioasid)
>   - Allocate a PASID and associate a @private data with this
>     PASID. The PASID value is stored in @ioaisd if returning
>     success.
> 
> * iommu_pasid_free(pasid, ioasid)
>   - Free a PASID to the pool so that it could be consumed by
>     others.
> 
> This also adds below helpers to lookup or iterate PASID items
> associated with a consumer.
> 
> * iommu_pasid_for_each(pasid, func, data)
>   - Iterate PASID items of the consumer identified by @pasid,
>     and call @func() against each item. An error returned from
>     @func() will break the iteration.
> 
> * iommu_pasid_find(pasid, ioasid)
>   - Retrieve the private data associated with @ioasid.
> 
> Cc: Ashok Raj <ashok.raj@xxxxxxxxx>
> Cc: Jacob Pan <jacob.jun.pan@xxxxxxxxxxxxxxx>
> Cc: Kevin Tian <kevin.tian@xxxxxxxxx>
> Cc: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/Kconfig |  1 +
>  drivers/iommu/iommu.c | 89
> +++++++++++++++++++++++++++++++++++++++++++ include/linux/iommu.h |
> 73 +++++++++++++++++++++++++++++++++++ 3 files changed, 163
> insertions(+)
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index d9a25715650e..39f2bb76c7b8 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -1,6 +1,7 @@
>  # IOMMU_API always gets selected by whoever wants it.
>  config IOMMU_API
>  	bool
> +	select IOASID
>  
>  menuconfig IOMMU_SUPPORT
>  	bool "IOMMU Hardware Support"
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 0b7c96d1425e..570b244897bb 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -2082,3 +2082,92 @@ void iommu_detach_device_aux(struct
> iommu_domain *domain, struct device *dev) }
>  }
>  EXPORT_SYMBOL_GPL(iommu_detach_device_aux);
> +
> +/*
> + * APIs for PASID used by IOMMU and the device drivers which depend
> + * on IOMMU.
> + */
> +struct iommu_pasid *iommu_pasid_init(struct bus_type *bus)
> +{
> +	struct iommu_pasid *pasid;
> +	int ret;
> +
> +	if (!bus || !bus->iommu_ops)
> +		return NULL;
> +
> +	pasid = kzalloc(sizeof(*pasid), GFP_KERNEL);
> +	if (!pasid)
> +		return NULL;
> +
> +	pasid->ops = bus->iommu_ops;
> +	/*
> +	 * The default range of an IOMMU PASID is from 0 to the full
> +	 * 20bit integer.
> +	 */
> +	pasid->min = 0;
> +	pasid->max = 0x100000;
> +	/*
> +	 * Give vendor specific iommu drivers a chance to set the
> pasid
> +	 * limits imposed by the iommu hardware.
> +	 */
> +	if (bus->iommu_ops->pasid_init) {
> +		ret = bus->iommu_ops->pasid_init(pasid);
> +		if (ret) {
> +			kfree(pasid);
> +			return NULL;
> +		}
> +	}
> +
> +	return pasid;
> +}
> +EXPORT_SYMBOL_GPL(iommu_pasid_init);
> +
> +void iommu_pasid_exit(struct iommu_pasid *pasid)
> +{
> +	kfree(pasid);
> +}
> +EXPORT_SYMBOL_GPL(iommu_pasid_exit);
> +
> +int iommu_pasid_alloc(struct iommu_pasid *pasid, ioasid_t min,
> +		      ioasid_t max, void *private, ioasid_t *ioasid)
> +{
> +	ioasid_t start, end, hw, val;
> +	int ret = -EAGAIN;
> +
> +	start = max_t(int, min, pasid->min);
> +	end = min_t(int, max, pasid->max);
> +
> +	if (pasid->ops->pasid_alloc)
> +		ret = pasid->ops->pasid_alloc(pasid, start, end,
> &hw); +
> +	if (ret == -EAGAIN)
> +                val = ioasid_alloc(&pasid->set, start, end, private);
> +	else if (ret == 0)
> +		val = ioasid_alloc(&pasid->set, hw, hw + 1, private);
this may fail due to conflict with other callers of ioasic_alloc(), but
we should really respect the iommu ops allocator. If we move the
pasid_alloc op into ioasid code, then we don't need to worry about the
conflict.
> +	else
> +		goto hw_ret;
> +
> +	if (val == INVALID_IOASID)
> +		goto ioasid_ret;
> +
> +	*ioasid = val;
> +
> +        return 0;
> +
> +ioasid_ret:
> +	if (pasid->ops->pasid_free)
> +		pasid->ops->pasid_free(pasid, hw);
> +
> +hw_ret:
> +	return -ENODEV;
> +}
> +EXPORT_SYMBOL_GPL(iommu_pasid_alloc);
> +
> +void iommu_pasid_free(struct iommu_pasid *pasid, ioasid_t ioasid)
> +{
> +	if (pasid->ops->pasid_free)
> +		pasid->ops->pasid_free(pasid, ioasid);
> +
> +	ioasid_free(ioasid);
> +}
> +EXPORT_SYMBOL_GPL(iommu_pasid_free);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 9bf1b3f2457a..4f5202c8170b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -20,6 +20,7 @@
>  #define __LINUX_IOMMU_H
>  
>  #include <linux/scatterlist.h>
> +#include <linux/ioasid.h>
>  #include <linux/device.h>
>  #include <linux/types.h>
>  #include <linux/errno.h>
> @@ -48,6 +49,7 @@ struct bus_type;
>  struct device;
>  struct iommu_domain;
>  struct notifier_block;
> +struct iommu_pasid;
>  
>  /* iommu fault flags */
>  #define IOMMU_FAULT_READ	0x0
> @@ -194,6 +196,9 @@ enum iommu_dev_attr {
>   * @of_xlate: add OF master IDs to iommu grouping
>   * @get_dev_attr: get per device IOMMU attributions
>   * @set_dev_attr: set per device IOMMU attributions
> + * @pasid_init: initialize a pasid consumer
> + * @pasid_alloc: allocate a pasid from low level driver
> + * @pasid_free: free a pasid to low level driver
>   * @pgsize_bitmap: bitmap of all possible supported page sizes
>   */
>  struct iommu_ops {
> @@ -246,6 +251,12 @@ struct iommu_ops {
>  	int (*attach_dev_aux)(struct iommu_domain *domain, struct
> device *dev); void (*detach_dev_aux)(struct iommu_domain *domain,
> struct device *dev); 
> +	/* IOMMU pasid callbacks */
> +	int (*pasid_init)(struct iommu_pasid *pasid);
> +	int (*pasid_alloc)(struct iommu_pasid *pasid, ioasid_t start,
> +			   ioasid_t end, ioasid_t *ioasid);
> +	void (*pasid_free)(struct iommu_pasid *pasid, ioasid_t
> ioasid); +
>  	unsigned long pgsize_bitmap;
>  };
>  
> @@ -428,12 +439,41 @@ extern int iommu_attach_device_aux(struct
> iommu_domain *domain, extern void iommu_detach_device_aux(struct
> iommu_domain *domain, struct device *dev);
>  
> +/*
> + * Per IOMMU PASID consumer data.
> + */
> +struct iommu_pasid {
> +	ioasid_t		max;
> +	ioasid_t		min;
> +	struct ioasid_set	set;
> +	const struct iommu_ops	*ops;
> +
> +	/* vendor specific iommu private data */
> +	void			*priv;
> +};
> +
> +struct iommu_pasid *iommu_pasid_init(struct bus_type *bus);
> +void iommu_pasid_exit(struct iommu_pasid *pasid);
> +int iommu_pasid_alloc(struct iommu_pasid *pasid, ioasid_t min,
> +		      ioasid_t max, void *private, ioasid_t *ioasid);
> +void iommu_pasid_free(struct iommu_pasid *pasid, ioasid_t iosid);
> +static inline int
> +iommu_pasid_for_each(struct iommu_pasid *pasid, ioasid_iter_t func,
> void *data) +{
> +	return ioasid_for_each(&pasid->set, func, data);
> +}
> +static inline void*
> +iommu_pasid_find(struct iommu_pasid *pasid, ioasid_t ioasid)
> +{
> +	return ioasid_find(&pasid->set, ioasid);
> +}
>  #else /* CONFIG_IOMMU_API */
>  
>  struct iommu_ops {};
>  struct iommu_group {};
>  struct iommu_fwspec {};
>  struct iommu_device {};
> +struct iommu_pasid {};
>  
>  static inline bool iommu_present(struct bus_type *bus)
>  {
> @@ -734,6 +774,39 @@ static inline void
>  iommu_detach_device_aux(struct iommu_domain *domain, struct device
> *dev) {
>  }
> +
> +static inline struct iommu_pasid *
> +iommu_pasid_init(struct bus_type *bus)
> +{
> +	return NULL;
> +}
> +
> +static inline void iommu_pasid_exit(struct iommu_pasid *pasid)
> +{
> +}
> +
> +static inline int
> +iommu_pasid_alloc(struct iommu_pasid *pasid, ioasid_t min,
> +		  ioasid_t max, void *private, ioasid_t *ioasid)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline void iommu_pasid_free(struct iommu_pasid *pasid,
> ioasid_t iosid) +{
> +}
> +
> +static inline int
> +iommu_pasid_for_each(struct iommu_pasid *pasid, ioasid_iter_t func,
> void *data) +{
> +	return -ENODEV;
> +}
> +
> +static inline void*
> +iommu_pasid_find(struct iommu_pasid *pasid, ioasid_t ioasid)
> +{
> +	return NULL;
> +}
>  #endif /* CONFIG_IOMMU_API */
>  
>  #ifdef CONFIG_IOMMU_DEBUGFS

[Jacob Pan]