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

From: Alexey Kardashevskiy <[email-masked]>
Date: Thu, 02 Apr 2015 13:33:57 +1100

On 04/02/2015 08:48 AM, Alex Williamson wrote:
> 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.

Cannot argue with that but it is kind of late or not for this patchset, no? 
And iommu_table is way too generic for powerpc/spapr-specific thing.

I can replace with something better, should I do this now?

> (sorry for commenting twice on the same patch)
>

-- 
Alexey