RE: [PATCH 01/37] iommu: Introduce Shared Virtual Addressing API

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> From: Jean-Philippe Brucker
> Sent: Tuesday, February 13, 2018 2:33 AM
> 
> Shared Virtual Addressing (SVA) provides a way for device drivers to bind
> process address spaces to devices. This requires the IOMMU to support the
> same page table format as CPUs, and requires the system to support I/O

"same" is a bit restrictive. "compatible" is better as you used in coverletter. :-)

> Page Faults (IOPF) and Process Address Space ID (PASID). When all of these
> are available, DMA can access virtual addresses of a process. A PASID is
> allocated for each process, and the device driver programs it into the
> device in an implementation-specific way.
> 
> Add a new API for sharing process page tables with devices. Introduce two
> IOMMU operations, sva_device_init() and sva_device_shutdown(), that
> prepare the IOMMU driver for SVA. For example allocate PASID tables and
> fault queues. Subsequent patches will implement the bind() and unbind()
> operations.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> ---
>  drivers/iommu/Kconfig     | 10 ++++++
>  drivers/iommu/Makefile    |  1 +
>  drivers/iommu/iommu-sva.c | 90
> +++++++++++++++++++++++++++++++++++++++++++++++
>  include/linux/iommu.h     | 32 +++++++++++++++++
>  4 files changed, 133 insertions(+)
>  create mode 100644 drivers/iommu/iommu-sva.c
> 
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index f3a21343e636..555147a61f7c 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -74,6 +74,16 @@ config IOMMU_DMA
>  	select IOMMU_IOVA
>  	select NEED_SG_DMA_LENGTH
> 
> +config IOMMU_SVA
> +	bool "Shared Virtual Addressing API for the IOMMU"
> +	select IOMMU_API
> +	help
> +	  Enable process address space management for the IOMMU API. In
> systems
> +	  that support it, device drivers can bind process address spaces to
> +	  devices and share their page tables using this API.

"their page table" is a bit confusing here.

> +
> +	  If unsure, say N here.
> +
>  config FSL_PAMU
>  	bool "Freescale IOMMU support"
>  	depends on PCI
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 1fb695854809..1dbcc89ebe4c 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -3,6 +3,7 @@ obj-$(CONFIG_IOMMU_API) += iommu.o
>  obj-$(CONFIG_IOMMU_API) += iommu-traces.o
>  obj-$(CONFIG_IOMMU_API) += iommu-sysfs.o
>  obj-$(CONFIG_IOMMU_DMA) += dma-iommu.o
> +obj-$(CONFIG_IOMMU_SVA) += iommu-sva.o
>  obj-$(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
> diff --git a/drivers/iommu/iommu-sva.c b/drivers/iommu/iommu-sva.c
> new file mode 100644
> index 000000000000..cab5d723520f
> --- /dev/null
> +++ b/drivers/iommu/iommu-sva.c
> @@ -0,0 +1,90 @@
> +/*
> + * Track processes address spaces bound to devices and allocate PASIDs.
> + *
> + * Copyright (C) 2018 ARM Ltd.
> + * Author: Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx>
> + *
> + * SPDX-License-Identifier: GPL-2.0
> + */
> +
> +#include <linux/iommu.h>
> +
> +/**
> + * iommu_sva_device_init() - Initialize Shared Virtual Addressing for a
> device
> + * @dev: the device
> + * @features: bitmask of features that need to be initialized
> + * @max_pasid: max PASID value supported by the device
> + *
> + * Users of the bind()/unbind() API must call this function to initialize all
> + * features required for SVA.
> + *
> + * - If the device should support multiple address spaces (e.g. PCI PASID),
> + *   IOMMU_SVA_FEAT_PASID must be requested.

I think it is by default assumed when using this API, based on definition of
SVA. Can you elaborate the situation where this flag can be cleared?

> + *
> + *   By default the PASID allocated during bind() is limited by the IOMMU
> + *   capacity, and by the device PASID width defined in the PCI capability or
> in
> + *   the firmware description. Setting @max_pasid to a non-zero value
> smaller
> + *   than this limit overrides it.
> + *
> + * - If the device should support I/O Page Faults (e.g. PCI PRI),
> + *   IOMMU_SVA_FEAT_IOPF must be requested.
> + *
> + * The device should not be be performing any DMA while this function is

remove double "be"

> + * running.

"otherwise the behavior is undefined"

> + *
> + * Return 0 if initialization succeeded, or an error.
> + */
> +int iommu_sva_device_init(struct device *dev, unsigned long features,
> +			  unsigned int max_pasid)
> +{
> +	int ret;
> +	unsigned int min_pasid = 0;
> +	struct iommu_param *dev_param = dev->iommu_param;
> +	struct iommu_domain *domain =
> iommu_get_domain_for_dev(dev);
> +
> +	if (!domain || !dev_param || !domain->ops->sva_device_init)
> +		return -ENODEV;
> +
> +	/*
> +	 * IOMMU driver updates the limits depending on the IOMMU and
> device
> +	 * capabilities.
> +	 */
> +	ret = domain->ops->sva_device_init(dev, features, &min_pasid,
> +					   &max_pasid);
> +	if (ret)
> +		return ret;
> +
> +	/* FIXME: racy. Next version should have a mutex (same as fault
> handler) */
> +	dev_param->sva_features = features;
> +	dev_param->min_pasid = min_pasid;
> +	dev_param->max_pasid = max_pasid;

what's the point of min_pasid here?

> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_device_init);
> +
> +/**
> + * iommu_sva_device_shutdown() - Shutdown Shared Virtual Addressing
> for a device
> + * @dev: the device
> + *
> + * Disable SVA. The device should not be performing any DMA while this
> function
> + * is running.
> + */
> +int iommu_sva_device_shutdown(struct device *dev)
> +{
> +	struct iommu_param *dev_param = dev->iommu_param;
> +	struct iommu_domain *domain =
> iommu_get_domain_for_dev(dev);
> +
> +	if (!domain)
> +		return -ENODEV;
> +
> +	if (domain->ops->sva_device_shutdown)
> +		domain->ops->sva_device_shutdown(dev);
> +
> +	dev_param->sva_features = 0;
> +	dev_param->min_pasid = 0;
> +	dev_param->max_pasid = 0;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iommu_sva_device_shutdown);
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 66ef406396e9..e9e09eecdece 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -60,6 +60,11 @@ typedef int (*iommu_fault_handler_t)(struct
> iommu_domain *,
>  			struct device *, unsigned long, int, void *);
>  typedef int (*iommu_dev_fault_handler_t)(struct iommu_fault_event *,
> void *);
> 
> +/* Request PASID support */
> +#define IOMMU_SVA_FEAT_PASID		(1 << 0)
> +/* Request I/O page fault support */
> +#define IOMMU_SVA_FEAT_IOPF		(1 << 1)
> +
>  struct iommu_domain_geometry {
>  	dma_addr_t aperture_start; /* First address that can be mapped
> */
>  	dma_addr_t aperture_end;   /* Last address that can be mapped
> */
> @@ -197,6 +202,8 @@ struct page_response_msg {
>   * @domain_free: free iommu domain
>   * @attach_dev: attach device to an iommu domain
>   * @detach_dev: detach device from an iommu domain
> + * @sva_device_init: initialize Shared Virtual Adressing for a device
> + * @sva_device_shutdown: shutdown Shared Virtual Adressing for a
> device
>   * @map: map a physically contiguous memory region to an iommu
> domain
>   * @unmap: unmap a physically contiguous memory region from an
> iommu domain
>   * @map_sg: map a scatter-gather list of physically contiguous memory
> chunks
> @@ -230,6 +237,10 @@ struct iommu_ops {
> 
>  	int (*attach_dev)(struct iommu_domain *domain, struct device
> *dev);
>  	void (*detach_dev)(struct iommu_domain *domain, struct device
> *dev);
> +	int (*sva_device_init)(struct device *dev, unsigned long features,
> +			       unsigned int *min_pasid,
> +			       unsigned int *max_pasid);
> +	void (*sva_device_shutdown)(struct device *dev);
>  	int (*map)(struct iommu_domain *domain, unsigned long iova,
>  		   phys_addr_t paddr, size_t size, int prot);
>  	size_t (*unmap)(struct iommu_domain *domain, unsigned long
> iova,
> @@ -385,6 +396,9 @@ struct iommu_fault_param {
>   */
>  struct iommu_param {
>  	struct iommu_fault_param *fault_param;
> +	unsigned long sva_features;
> +	unsigned int min_pasid;
> +	unsigned int max_pasid;
>  };
> 
>  int  iommu_device_register(struct iommu_device *iommu);
> @@ -878,4 +892,22 @@ const struct iommu_ops
> *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
> 
>  #endif /* CONFIG_IOMMU_API */
> 
> +#ifdef CONFIG_IOMMU_SVA
> +extern int iommu_sva_device_init(struct device *dev, unsigned long
> features,
> +				 unsigned int max_pasid);
> +extern int iommu_sva_device_shutdown(struct device *dev);
> +#else /* CONFIG_IOMMU_SVA */
> +static inline int iommu_sva_device_init(struct device *dev,
> +					unsigned long features,
> +					unsigned int max_pasid)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int iommu_sva_device_shutdown(struct device *dev)
> +{
> +	return -ENODEV;
> +}
> +#endif /* CONFIG_IOMMU_SVA */
> +
>  #endif /* __LINUX_IOMMU_H */
> --
> 2.15.1
> 
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> https://lists.linuxfoundation.org/mailman/listinfo/iommu
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