Re: [PATCH V6 00/14] powerpc/vas: Page fault handling for user space NX requests

On 5/3/20 7:21 am, Haren Myneni wrote:

On power9, Virtual Accelerator Switchboard (VAS) allows user space or
kernel to communicate with Nest Accelerator (NX) directly using COPY/PASTE
instructions. NX provides various functionalities such as compression,
encryption and etc. But only compression (842 and GZIP formats) is
supported in Linux kernel on power9.

842 compression driver (drivers/crypto/nx/nx-842-powernv.c)
is already included in Linux. Only GZIP support will be available from
user space.

Applications can issue GZIP compression / decompression requests to NX with
COPY/PASTE instructions. When NX is processing these requests, can hit
fault on the request buffer (not in memory). It issues an interrupt and
pastes fault CRB in fault FIFO. Expects kernel to handle this fault and
return credits for both send and fault windows after processing.

This patch series adds IRQ and fault window setup, and NX fault handling:
- Alloc IRQ and trigger port address, and configure IRQ per VAS instance.
- Set port# for each window to generate an interrupt when noticed fault.
- Set fault window and FIFO on which NX paste fault CRB.
- Setup IRQ thread fault handler per VAS instance.
- When receiving an interrupt, Read CRBs from fault FIFO and update
   coprocessor_status_block (CSB) in the corresponding CRB with translation
   failure (CSB_CC_TRANSLATION). After issuing NX requests, process polls
   on CSB address. When it sees translation error, can touch the request
   buffer to bring the page in to memory and reissue NX request.
- If copy_to_user fails on user space CSB address, OS sends SEGV signal.

Tested these patches with NX-GZIP support and will be posting this series
soon.

Patches 1 & 2: Define alloc IRQ and get port address per chip which are needed
                to alloc IRQ per VAS instance.
Patch 3: Define nx_fault_stamp on which NX writes fault status for the fault
          CRB
Patch 4: Alloc and setup IRQ and trigger port address for each VAS instance
Patch 5: Setup fault window per each VAS instance. This window is used for
          NX to paste fault CRB in FIFO.
Patches 6 & 7: Setup threaded IRQ per VAS and register NX with fault window
          ID and port number for each send window so that NX paste fault CRB
          in this window.
Patch 8: Reference to pid and mm so that pid is not used until window closed.
          Needed for multi thread application where child can open a window
          and can be used by parent later.
Patches 9 and 10: Process CRBs from fault FIFO and notify tasks by
          updating CSB or through signals.
Patches 11 and 12: Return credits for send and fault windows after handling
         faults.
Patch 14:Fix closing send window after all credits are returned. This issue
          happens only for user space requests. No page faults on kernel
          request buffer.

This series adds a bunch of sparse warnings - it would be great if you 
could take a look.

https://openpower.xyz/job/snowpatch/job/snowpatch-linux-sparse/16052//artifact/linux/report.txt

-- 
Andrew Donnellan              OzLabs, ADL Canberra
ajd@linux.ibm.com             IBM Australia Limited