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

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

On Sat, 2015-03-28 at 01:54 +1100, Alexey Kardashevskiy wrote:

quoted

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 <redacted>
---
  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