Re: [RFC 01/13] iommu: Introduce bind_guest_stage API

[Auger Eric <eric.auger@redhat.com>]

Hi,

On 08/23/2018 02:17 PM, Eric Auger wrote:
> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
> 
> In virtualization use case, when a guest is assigned
> a PCI host device, protected by a virtual IOMMU on a guest,
> the physical IOMMU must be programmed to be consistent with
> the guest mappings. If the physical IOMMU supports two
> translation stages it makes sense to program guest mappings
> onto the first stage while to host owns the stage 2.
> 
> In that case, it is mandated to trap on guest configuration
> settings and pass those to the physical iommu driver.
> 
> This patch adds a new API to the iommu subsystem that allows
> to bind and unbind the guest configuration data to the host.
> 
> A generic iommu_guest_stage_config struct is introduced in
> a new iommu.h uapi header. This is going to be used by the VFIO
> user API. We foresee at least 2 specialization of this struct,
> for PASID table passing and ARM SMMUv3.
> 
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> 
> ---
> 
> This patch generalizes the API introduced by Jacob & co-authors in
> https://lwn.net/Articles/754331/
> ---
>  drivers/iommu/iommu.c      | 19 +++++++++++++++
>  include/linux/iommu.h      | 23 ++++++++++++++++++
>  include/uapi/linux/iommu.h | 59 ++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 101 insertions(+)
>  create mode 100644 include/uapi/linux/iommu.h
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 63b3756..5156172 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -1326,6 +1326,25 @@ int iommu_attach_device(struct iommu_domain *domain, struct device *dev)
>  }
>  EXPORT_SYMBOL_GPL(iommu_attach_device);
>  
> +int iommu_bind_guest_stage(struct iommu_domain *domain, struct device *dev,
> +			   struct iommu_guest_stage_config *cfg)
> +{
> +	if (unlikely(!domain->ops->bind_guest_stage))
> +		return -ENODEV;
> +
> +	return domain->ops->bind_guest_stage(domain, dev, cfg);
> +}
> +EXPORT_SYMBOL_GPL(iommu_bind_guest_stage);
> +
> +void iommu_unbind_guest_stage(struct iommu_domain *domain, struct device *dev)
> +{
> +	if (unlikely(!domain->ops->unbind_guest_stage))
> +		return;
> +
> +	domain->ops->unbind_guest_stage(domain, dev);
> +}
> +EXPORT_SYMBOL_GPL(iommu_unbind_guest_stage);
> +
>  static void __iommu_detach_device(struct iommu_domain *domain,
>  				  struct device *dev)
>  {
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 19938ee..aec853d 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -25,6 +25,7 @@
>  #include <linux/errno.h>
>  #include <linux/err.h>
>  #include <linux/of.h>
> +#include <uapi/linux/iommu.h>
>  
>  #define IOMMU_READ	(1 << 0)
>  #define IOMMU_WRITE	(1 << 1)
> @@ -187,6 +188,8 @@ struct iommu_resv_region {
>   * @domain_get_windows: Return the number of windows for a domain
>   * @of_xlate: add OF master IDs to iommu grouping
>   * @pgsize_bitmap: bitmap of all possible supported page sizes
> + * @bind_guest_stage: program the guest stage configuration
> + * @unbind_guest_stage: unbind the guest stage and restore defaults
>   */
>  struct iommu_ops {
>  	bool (*capable)(enum iommu_cap);
> @@ -235,6 +238,11 @@ struct iommu_ops {
>  	int (*of_xlate)(struct device *dev, struct of_phandle_args *args);
>  	bool (*is_attach_deferred)(struct iommu_domain *domain, struct device *dev);
>  
> +	int (*bind_guest_stage)(struct iommu_domain *domain, struct device *dev,
> +				struct iommu_guest_stage_config *cfg);
> +	void (*unbind_guest_stage)(struct iommu_domain *domain,
> +				   struct device *dev);
> +
>  	unsigned long pgsize_bitmap;
>  };
>  
> @@ -296,6 +304,10 @@ extern int iommu_attach_device(struct iommu_domain *domain,
>  			       struct device *dev);
>  extern void iommu_detach_device(struct iommu_domain *domain,
>  				struct device *dev);
> +extern int iommu_bind_guest_stage(struct iommu_domain *domain,
> +		struct device *dev, struct iommu_guest_stage_config *cfg);
> +extern void iommu_unbind_guest_stage(struct iommu_domain *domain,
> +				     struct device *dev);
>  extern struct iommu_domain *iommu_get_domain_for_dev(struct device *dev);
>  extern int iommu_map(struct iommu_domain *domain, unsigned long iova,
>  		     phys_addr_t paddr, size_t size, int prot);
> @@ -696,6 +708,17 @@ const struct iommu_ops *iommu_ops_from_fwnode(struct fwnode_handle *fwnode)
>  	return NULL;
>  }
>  
> +static inline
> +int iommu_bind_guest_stage(struct iommu_domain *domain, struct device *dev,
> +			   struct iommu_guest_stage_config *cfg)
> +{
> +	return -ENODEV;
> +}
> +static inline
> +void iommu_unbind_guest_stage(struct iommu_domain *domain, struct device *dev)
> +{
> +}
> +
>  #endif /* CONFIG_IOMMU_API */
>  
>  #endif /* __LINUX_IOMMU_H */
> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
> new file mode 100644
> index 0000000..2d1593c
> --- /dev/null
> +++ b/include/uapi/linux/iommu.h
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +/*
> + * IOMMU user API definitions
> + *
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#ifndef _UAPI_IOMMU_H
> +#define _UAPI_IOMMU_H
> +
> +#include <linux/types.h>
> +
> +/**
> + * PASID table data used to bind guest PASID table to the host IOMMU. This will
> + * enable guest managed first level page tables.
> + * @version: for future extensions and identification of the data format
> + * @bytes: size of this structure
> + * @base_ptr:	PASID table pointer
> + * @pasid_bits:	number of bits supported in the guest PASID table, must be less
> + *		or equal than the host supported PASID size.
> + */
> +struct iommu_pasid_table_config {
> +	__u32 version;
> +#define PASID_TABLE_CFG_VERSION_1 1
> +	__u32 bytes;
> +	__u64 base_ptr;
> +	__u8 pasid_bits;
> +};
> +
> +/**
> + * Stream Table Entry S1 info
> + * @disabled: the smmu is disabled
> + * @bypassed: stage 1 is bypassed
> + * @aborted: aborted
> + * @cdptr_dma: GPA of the Context Descriptor
> + * @asid: address space identified associated to the CD
> + */
> +struct iommu_smmu_s1_config {
> +	__u8 disabled;
> +	__u8 bypassed;
> +	__u8 aborted;
> +	__u64 cdptr_dma;
> +	__u16 asid;
This asid field is a leftover. asid is part of the CD (owned by the
guest) and cannot be conveyed through this API. What is relevant is to
pass is the guest asid_bits (vSMMU IDR1 info), to be compared with the
host one. So we end up having something similar to the base_ptr and
pasid_bits of iommu_pasid_table_config.

Otherwise, the other fields (disable, bypassed, aborted) can be packed
as masks in a _u8 flag.

Anyway this API still is at the stage of proof of concept. At least it
shows the similarities between that use case and the PASID one and
should encourage to discuss about the relevance to have a unified API to
pass the guest stage info.

Thanks

Eric
> +};
> +
> +struct iommu_guest_stage_config {
> +#define PASID_TABLE	(1 << 0)
> +#define SMMUV3_S1_CFG	(1 << 1)
> +	__u32 flags;
> +	union {
> +		struct iommu_pasid_table_config pasidt;
> +		struct iommu_smmu_s1_config smmu_s1;
> +	};
> +};
> +
> +#endif /* _UAPI_IOMMU_H */
>