[PATCH v12 0/2] zfcp: Use DMA streaming API to map I/O

[M Nikhil <nikh1092@linux.ibm.com>]

In the existing zFCP driver, virtual addresses are translated directly
into bus (physical addresses) for DMA operations on all I/O buffers
passing from zFCP driver to the device.

Need for using DMA-API in zFCP driver:

In a Secure Execution environment, the host must ensure that device DMA
accesses are restricted to non-guest-private, page-sized memory blocks.
This prevents I/O failures that can occur when a device attempts to
access guest-private memory. Therefore, guest memory pages must be
prepared by the hypervisor before they become accessible to an I/O
device.

To support this requirement, the host Linux kernel must be reliably
informed whenever a memory region becomes eligible for device DMA access
and when that access must be revoked. This information must be
maintained correctly at least at page size granularity. To satisfy these
requirements, all I/O buffers used by the zFCP driver should be mapped
through the DMA API.

DMA API Integration in zFCP:

The zFCP driver is updated to use the DMA streaming API's to map all the
I/O buffers which will be passed to the device.
All zFCP I/O buffers (QTCB, SRB, CT/ELS and SCSI I/O) are represented as
scatter-gather lists and mapped through DMA API using dma_map_sgtable().
Once the DMA transfer is complete, the corresponding mappings are
released using dma_unmap_sgtable().

By routing all device-visible memory through the DMA mapping layer, the
driver ensures that:
1. DMA access is properly authorized before use.
2. DMA is revoked after use.
3. Secure Execution memory restrictions are honored.

Changes on the github can be found at:
https://github.ibm.com/M-Nikhil/linux/commits/zfcp_dma_api_implementation_io_path_version12

M Nikhil (2):
  zfcp: Replace sg-list with sg_table in zfcp_fsf_ct_els structure
  zfcp: Use DMA streaming API to map I/O

 drivers/s390/scsi/zfcp_aux.c  |  16 +++
 drivers/s390/scsi/zfcp_dbf.c  |  16 +--
 drivers/s390/scsi/zfcp_def.h  |   4 +
 drivers/s390/scsi/zfcp_ext.h  |  10 +-
 drivers/s390/scsi/zfcp_fc.c   |  36 +++--
 drivers/s390/scsi/zfcp_fsf.c  | 260 ++++++++++++++++++++++++++++------
 drivers/s390/scsi/zfcp_fsf.h  |   9 +-
 drivers/s390/scsi/zfcp_qdio.c |  37 +++--
 drivers/s390/scsi/zfcp_qdio.h |  27 ++--
 9 files changed, 321 insertions(+), 94 deletions(-)

-- 
2.53.0