When kernel panicked and jump into the kdump kernel, DMA started by the
1st kernel is not stopped, this is called on-flight DMA. In the current
code it will disable iommu and build new translation table and attach
device to it. This will cause:

 1. IO_PAGE_FAULT warning message can be seen.
 2. transfer data to or from incorrect areas of memory.

Sometime it causes the dump failure or kernel hang.

The principle of the fix is to copy the old device table to let the old-flight
DMA continue looking up to get correct address translation and irq remap result,
meanwhile to defer the assignment of device to domain to device driver 
initializtion
stage. The old domain ids used in 1st kernel are reserved. And a new call-back
is_attach_deferred() is added to iommu-ops, will check whether we need defer the
domain attach/detach in iommu-core code. If defer is needed, just return 
directly
from amd iommu attach/detach function. The attachment will be done in device 
driver
initializaiton stage when calling get_domain().

Change history:
v9->v10:
    Main changes are as follows according to Joerg's suggestion. The detailed
    changes will be added to each patch.
    - Drop the old patch 12/13 patch.

    - Move the old dev table copy out of iommu loop in copy_dev_tables().

    - Add global variable amd_iommu_pre_enabled to optimize code change
      when call copy_dev_tables().

v8->v9:
    Made changes according to Joerg's reviewing comments and suggestions:
    - Check if all IOMMUs are pre-enabled, otherwise do not copy dev table
      and just continue as normal kernel does.

    - Add a new global old_dev_tbl_cpy to point to a newly allocated device
      table. The content of old device table will be copied to the specific
      device table for copying which old_dev_tbl_cpy points at. If copy failed
      we can still use the amd_iommu_dev_table which is allocated in
      early_amd_iommu_init(). This is for better rolling back if copy failed,
      the amd_iommu_dev_table has got necessary initialization since iommu init.

    - Always allocate device table with GFP_DMA32 flag to make sure that they
      are under 4G. This tries to work around the issue mentioned in patch 
10/13.
      Meanwhile double check if the address of device table is above 4G since
      it could be touched accidentally in corrupted 1st kernel and not 
trustworthy
      any more.

v7->v8:
    Rebase patchset v7 on the latest v4.13-rc1.
    - And re-enable printing IO_PAGE_FAULT message in kdump kernel.

    - Only disable iommu if amd_iommu=off is specified in kdump kernel.


v6->v7:
    Two main changes are made according to Joerg's suggestion:
    - Add is_attach_deferred call-back to iommu-ops. With this domain
      can be deferred to device driver init cleanly.

    - Allocate memory below 4G for dev table if translation pre-enabled.
      AMD engineer pointed out that it's unsafe to update the device-table
      while iommu is enabled. device-table pointer update is split up into
      two 32bit writes in the IOMMU hardware. So updating it while the IOMMU
      is enabled could have some nasty side effects.

v5->v6:
    According to Joerg's comments made several below main changes:
    - Add sanity check when copy old dev tables.

    - If a device is set up with guest translations (DTE.GV=1), then don't
      copy that information but move the device over to an empty guest-cr3
      table and handle the faults in the PPR log (which just answer them
      with INVALID).

v5:
    bnx2 NIC can't reset itself during driver init. Post patch to reset
    it during driver init. IO_PAGE_FAULT can't be seen anymore.

    Below is link of v5 post.
    https://lists.linuxfoundation.org/pipermail/iommu/2016-September/018527.html


Baoquan He (12):
  iommu/amd: Detect pre enabled translation
  iommu/amd: add several helper functions
  Revert "iommu/amd: Suppress IO_PAGE_FAULTs in kdump kernel"
  iommu/amd: Define bit fields for DTE particularly
  iommu/amd: Add function copy_dev_tables()
  iommu/amd: copy old trans table from old kernel
  iommu/amd: Do sanity check for address translation and irq remap of
    old dev table entry
  iommu: Add is_attach_deferred call-back to iommu-ops
  iommu/amd: Use is_attach_deferred call-back
  iommu/amd: Allocate memory below 4G for dev table if translation
    pre-enabled
  iommu/amd: Don't copy GCR3 table root pointer
  iommu/amd: Disable iommu only if amd_iommu=off is specified

 drivers/iommu/amd_iommu.c       |  65 ++++++------
 drivers/iommu/amd_iommu_init.c  | 223 +++++++++++++++++++++++++++++++++++-----
 drivers/iommu/amd_iommu_proto.h |   2 +
 drivers/iommu/amd_iommu_types.h |  55 +++++++++-
 drivers/iommu/amd_iommu_v2.c    |  18 +++-
 drivers/iommu/iommu.c           |   8 ++
 include/linux/iommu.h           |   1 +
 7 files changed, 306 insertions(+), 66 deletions(-)

-- 
2.5.5

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