dmaengine: idxd: process user page faults for completion record
authorDave Jiang <dave.jiang@intel.com>
Fri, 7 Apr 2023 20:31:36 +0000 (13:31 -0700)
committerVinod Koul <vkoul@kernel.org>
Wed, 12 Apr 2023 17:48:45 +0000 (23:18 +0530)
commitc40bd7d9737bdcfb02d42765bc6c59b338151123
tree77d85ebb3c91ae538bd6c18d857f38dff6cc4546
parentb022f59725f0ae846191abbd6d2e611d7f60f826
dmaengine: idxd: process user page faults for completion record

DSA supports page fault handling through PRS. However, the DMA engine
that's processing the descriptor is blocked until the PRS response is
received. Other workqueues sharing the engine are also blocked.
Page fault handing by the driver with PRS disabled can be used to
mitigate the stalling.

With PRS disabled while ATS remain enabled, DSA handles page faults on
a completion record by reporting an event in the event log. In this
instance, the descriptor is completed and the event log contains the
completion record address and the contents of the completion record. Add
support to the event log handling code to fault in the completion record
and copy the content of the completion record to user memory.

A bitmap is introduced to keep track of discarded event log entries. When
the user process initiates ->release() of the char device, it no longer is
interested in any remaining event log entries tied to the relevant wq and
PASID. The driver will mark the event log entry index in the bitmap. Upon
encountering the entries during processing, the event log handler will just
clear the bitmap bit and skip the entry rather than attempt to process the
event log entry.

Tested-by: Tony Zhu <tony.zhu@intel.com>
Signed-off-by: Dave Jiang <dave.jiang@intel.com>
Co-developed-by: Fenghua Yu <fenghua.yu@intel.com>
Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Link: https://lore.kernel.org/r/20230407203143.2189681-10-fenghua.yu@intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>
drivers/dma/idxd/cdev.c
drivers/dma/idxd/device.c
drivers/dma/idxd/idxd.h
drivers/dma/idxd/init.c
drivers/dma/idxd/irq.c
include/uapi/linux/idxd.h