[PATCH v2 0/9] Add shared workqueue support for idxd driver

[Dave Jiang]

v2:
- Dropped device feature enabling (GregKH)
- Dropped PCI device feature enabling (Bjorn)
	- https://members.pcisig.com/wg/PCI-SIG/document/14237
	- After some internal discussion, we have decided to hold off on the
	  enabling of DMWR due to the following reasons. 1. Most first gen hw
	  will not have the feature bits. 2. First gen hw that support the
	  feature are all Root Complex integrated endpoints. 3. PCI devices
	  that are not RCiEPâs with this capability wonât surface for a few
	  years so we can wait until we can test the full code.
- Dropped special ioremap (hch)
- Added proper support for WQ flush (tony, dan)
- Changed descriptor submission to use sbitmap_queue for blocking. (dan)
- Split out MOBDIR64B to right location for ENQCMDS placement. (daveh)
- Split out SVM kernel dependencies for driver. (daveh)
- Call enqcmds() directly (daveh)
- Fix enqcmds() commit log (daveh)
- Split out fault processing code (tony)

Driver stage 1 postings for context: [1]

The patch series has functionality dependency on Fenghua's "Tag application
address space for devices" patch series for the ENQCMD CPU command enumeration
and the PASID MSR support. [2]

The first patch enumerating ENQCMD is lifted from Fenghua's patch series. It
removes the compilation dependency for the driver. It can be dropped by the
maintainer merging the driver patch series once Fenghua's patch series is
merged.

== Background ==
A typical DMA device requires the driver to translate application buffers to
hardware addresses, and a kernel-user transition to notify the hardware of new
work. Shared Virtual Addressing (SVA) allows the processor and device to use the
same virtual addresses without requiring software to translate between the
address spaces. ENQCMD is a new instruction on Intel Platforms that allows user
applications to directly notify hardware of new work, much like how doorbells
are used in some hardware, but it carries a payload along with it. ENQCMDS is
the supervisor version (ring0) of ENQCMD.

== ENQCMDS ==
Introduce iosubmit_cmd512_sync(), a common wrapper that copies an input payload
to a 64B aligned destination and confirms whether the payload was accepted by
the device or not. iosubmit_cmd512_sync() wraps the new ENQCMDS CPU instruction.
The ENQCMDS is a ring 0 CPU instruction that performs similar to the ENQCMD
instruction. Descriptor submission must use ENQCMD(S) for shared workqueues
(swq) on an Intel DSA device. 

== Shared WQ support ==
Introduce shared workqueue (swq) support for the idxd driver. The current idxd
driver contains dedicated workqueue (dwq) support only. A dwq accepts
descriptors from a MOVDIR64B instruction. MOVDIR64B is a posted instruction on
the PCIe bus, it does not wait for any response from the device. If the wq is
full, submitted descriptors are dropped. A swq utilizes the ENQCMDS in ring 0,
which is a non-posted instruction. The zero flag would be set to 1 if the device
rejects the descriptor or if the wq is full. A swq can be shared between
multiple users (kernel or userspace) due to not having to keep track of the wq
full condition for submission. A swq requires PASID and can only run with SVA
support. 

== IDXD SVA support ==
Add utilization of PASID to support Shared Virtual Addressing (SVA). With PASID
support, the descriptors can be programmed with host virtual address (HVA)
rather than IOVA. The hardware will work with the IOMMU in fulfilling page
requests. With SVA support, a user app using the char device interface can now
submit descriptors without having to pin the virtual memory range it wants to
DMA in its own address space. 

The series does not add SVA support for the dmaengine subsystem. That support
is coming at a later time.

[1]: https://lore.kernel.org/lkml/157965011794.73301.15960052071729101309.stgit@xxxxxxxxxxxxxxxxxxxxxxxxxx/
[2]: https://lore.kernel.org/lkml/1585596788-193989-1-git-send-email-fenghua.yu@xxxxxxxxx/
[3]: https://software.intel.com/en-us/articles/intel-sdm
[4]: https://software.intel.com/en-us/download/intel-scalable-io-virtualization-technical-specification
[5]: https://software.intel.com/en-us/download/intel-data-streaming-accelerator-preliminary-architecture-specification
[6]: https://01.org/blogs/2019/introducing-intel-data-streaming-accelerator
[7]: https://intel.github.io/idxd/
[8]: https://github.com/intel/idxd-driver idxd-stage2

---

Dave Jiang (8):
      x86/asm: move the raw asm in iosubmit_cmds512() to special_insns.h
      x86/asm: add enqcmds() to support ENQCMDS instruction
      dmaengine: idxd: add work queue drain support
      dmaengine: idxd: move submission to sbitmap_queue
      dmaengine: idxd: add shared workqueue support
      dmaengine: idxd: clean up descriptors with fault error
      dmaengine: idxd: add leading / for sysfspath in ABI documentation
      dmaengine: idxd: add ABI documentation for shared wq

Fenghua Yu (1):
      x86/cpufeatures: Enumerate ENQCMD and ENQCMDS instructions


 Documentation/ABI/stable/sysfs-driver-dma-idxd |   68 ++++--
 arch/x86/include/asm/cpufeatures.h             |    1 
 arch/x86/include/asm/io.h                      |   43 +++-
 arch/x86/include/asm/special_insns.h           |   17 ++
 arch/x86/kernel/cpu/cpuid-deps.c               |    1 
 drivers/dma/Kconfig                            |   15 +
 drivers/dma/idxd/cdev.c                        |   38 ++++
 drivers/dma/idxd/device.c                      |  252 +++++++++++++++---------
 drivers/dma/idxd/dma.c                         |    9 -
 drivers/dma/idxd/idxd.h                        |   32 ++-
 drivers/dma/idxd/init.c                        |  122 +++++++-----
 drivers/dma/idxd/irq.c                         |  184 ++++++++++++++----
 drivers/dma/idxd/registers.h                   |   14 +
 drivers/dma/idxd/submit.c                      |  105 ++++++----
 drivers/dma/idxd/sysfs.c                       |  150 +++++++++++++-
 15 files changed, 758 insertions(+), 293 deletions(-)

--