Subject: Re: [PATCH kernel v7 12/31] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table_group

From: Alex Williamson <[email-masked]>
Date: Wed, 01 Apr 2015 15:48:31 -0600

On Sat, 2015-03-28 at 01:54 +1100, Alexey Kardashevskiy wrote:
> Modern IBM POWERPC systems support multiple (currently two) TCE tables
> per IOMMU group (a.k.a. PE). This adds a iommu_table_group container
> for TCE tables. Right now just one table is supported.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> ---
>  Documentation/vfio.txt                      |  23 ++++++
>  arch/powerpc/include/asm/iommu.h            |  18 +++--
>  arch/powerpc/kernel/iommu.c                 |  34 ++++----
>  arch/powerpc/platforms/powernv/pci-ioda.c   |  38 +++++----
>  arch/powerpc/platforms/powernv/pci-p5ioc2.c |  17 ++--
>  arch/powerpc/platforms/powernv/pci.c        |   2 +-
>  arch/powerpc/platforms/powernv/pci.h        |   4 +-
>  arch/powerpc/platforms/pseries/iommu.c      |   9 ++-
>  drivers/vfio/vfio_iommu_spapr_tce.c         | 120 ++++++++++++++++++++--------
>  9 files changed, 183 insertions(+), 82 deletions(-)
> 
> diff --git a/Documentation/vfio.txt b/Documentation/vfio.txt
> index 96978ec..94328c8 100644
> --- a/Documentation/vfio.txt
> +++ b/Documentation/vfio.txt
> @@ -427,6 +427,29 @@ The code flow from the example above should be slightly changed:
>  
>  	....
>  
> +5) There is v2 of SPAPR TCE IOMMU. It deprecates VFIO_IOMMU_ENABLE/
> +VFIO_IOMMU_DISABLE and implements 2 new ioctls:
> +VFIO_IOMMU_SPAPR_REGISTER_MEMORY and VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY
> +(which are unsupported in v1 IOMMU).
> +
> +PPC64 paravirtualized guests generate a lot of map/unmap requests,
> +and the handling of those includes pinning/unpinning pages and updating
> +mm::locked_vm counter to make sure we do not exceed the rlimit.
> +The v2 IOMMU splits accounting and pinning into separate operations:
> +
> +- VFIO_IOMMU_SPAPR_REGISTER_MEMORY/VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY ioctls
> +receive a user space address and size of the block to be pinned.
> +Bisecting is not supported and VFIO_IOMMU_UNREGISTER_MEMORY is expected to
> +be called with the exact address and size used for registering
> +the memory block. The userspace is not expected to call these often.
> +The ranges are stored in a linked list in a VFIO container.
> +
> +- VFIO_IOMMU_MAP_DMA/VFIO_IOMMU_UNMAP_DMA ioctls only update the actual
> +IOMMU table and do not do pinning; instead these check that the userspace
> +address is from pre-registered range.
> +
> +This separation helps in optimizing DMA for guests.
> +
>  -------------------------------------------------------------------------------
>  
>  [1] VFIO was originally an acronym for "Virtual Function I/O" in its
> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> index eb75726..667aa1a 100644
> --- a/arch/powerpc/include/asm/iommu.h
> +++ b/arch/powerpc/include/asm/iommu.h
> @@ -90,9 +90,7 @@ struct iommu_table {
>  	struct iommu_pool pools[IOMMU_NR_POOLS];
>  	unsigned long *it_map;       /* A simple allocation bitmap for now */
>  	unsigned long  it_page_shift;/* table iommu page size */
> -#ifdef CONFIG_IOMMU_API
> -	struct iommu_group *it_group;
> -#endif
> +	struct iommu_table_group *it_group;
>  	struct iommu_table_ops *it_ops;
>  	void (*set_bypass)(struct iommu_table *tbl, bool enable);
>  };
> @@ -126,14 +124,24 @@ extern void iommu_free_table(struct iommu_table *tbl, const char *node_name);
>   */
>  extern struct iommu_table *iommu_init_table(struct iommu_table * tbl,
>  					    int nid);
> +
> +#define IOMMU_TABLE_GROUP_MAX_TABLES	1
> +
> +struct iommu_table_group {
>  #ifdef CONFIG_IOMMU_API
> -extern void iommu_register_group(struct iommu_table *tbl,
> +	struct iommu_group *group;
> +#endif
> +	struct iommu_table tables[IOMMU_TABLE_GROUP_MAX_TABLES];
> +};
> +
> +#ifdef CONFIG_IOMMU_API
> +extern void iommu_register_group(struct iommu_table_group *table_group,
>  				 int pci_domain_number, unsigned long pe_num);
>  extern int iommu_add_device(struct device *dev);
>  extern void iommu_del_device(struct device *dev);
>  extern int __init tce_iommu_bus_notifier_init(void);
>  #else
> -static inline void iommu_register_group(struct iommu_table *tbl,
> +static inline void iommu_register_group(struct iommu_table_group *table_group,
>  					int pci_domain_number,
>  					unsigned long pe_num)

Not a new problem, but there's some awfully liberal use of the namespace
with function names here.  IOMMU API uses iommu_foo() functions.  IOMMU
group related interfaces within the IOMMU API include "group" somewhere
in that name.  powerpc specific functions should include a tag to avoid
causing conflicts there.

(sorry for commenting twice on the same patch)