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

[Andrew Donnellan]

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 at linux.ibm.com             IBM Australia Limited