On Mon, Sep 03, 2018 at 10:32:16AM +0800, Lu Baolu wrote:

Date: Mon, 3 Sep 2018 10:32:16 +0800
From: Lu Baolu <baolu.lu@linux.intel.com>
To: Kenneth Lee <redacted>, Jonathan Corbet <corbet@lwn.net>,
 Herbert Xu [off-list ref], "David S . Miller"
 [off-list ref], Joerg Roedel [off-list ref], Alex Williamson
 [off-list ref], Kenneth Lee [off-list ref], Hao
 Fang [off-list ref], Zhou Wang [off-list ref], Zaibo Xu
 [off-list ref], Philippe Ombredanne [off-list ref], Greg
 Kroah-Hartman [off-list ref], Thomas Gleixner
 [off-list ref], linux-doc@vger.kernel.org,
 linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org,
 iommu@lists.linux-foundation.org, kvm@vger.kernel.org,
 linux-accelerators@lists.ozlabs.org, Sanjay Kumar
 [off-list ref]
CC: baolu.lu@linux.intel.com, linuxarm@huawei.com
Subject: Re: [RFCv2 PATCH 0/7] A General Accelerator Framework, WarpDrive
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Message-ID: [ref]

Hi,

On 09/03/2018 08:51 AM, Kenneth Lee wrote:

quoted

From: Kenneth Lee <redacted>

WarpDrive is an accelerator framework to expose the hardware capabilities
directly to the user space. It makes use of the exist vfio and vfio-mdev
facilities. So the user application can send request and DMA to the
hardware without interaction with the kernel. This removes the latency
of syscall.

WarpDrive is the name for the whole framework. The component in kernel
is called SDMDEV, Share Domain Mediated Device. Driver driver exposes its
hardware resource by registering to SDMDEV as a VFIO-Mdev. So the user
library of WarpDrive can access it via VFIO interface.

The patchset contains document for the detail. Please refer to it for more
information.

This patchset is intended to be used with Jean Philippe Brucker's SVA
patch [1], which enables not only IO side page fault, but also PASID
support to IOMMU and VFIO.

With these features, WarpDrive can support non-pinned memory and
multi-process in the same accelerator device.  We tested it in our SoC
integrated Accelerator (board ID: D06, Chip ID: HIP08). A reference work
tree can be found here: [2].

But it is not mandatory. This patchset is tested in the latest mainline
kernel without the SVA patches.  So it supports only one process for each
accelerator.

We have noticed the IOMMU aware mdev RFC announced recently [3].

The IOMMU aware mdev has similar idea but different intention comparing to
WarpDrive. It intends to dedicate part of the hardware resource to a VM.
And the design is supposed to be used with Scalable I/O Virtualization.
While sdmdev is intended to share the hardware resource with a big amount
of processes.  It just requires the hardware supporting address
translation per process (PCIE's PASID or ARM SMMU's substream ID).

But we don't see serious confliction on both design. We believe they can be
normalized as one.

The patch 1 is document of the framework. The patch 2 and 3 add sdmdev
support. The patch 4, 5 and 6 is drivers for Hislicon's ZIP Accelerator
which is registered to both crypto and warpdrive(sdmdev) and can be
used from kernel or user space at the same time. The patch 7 is a user
space sample demonstrating how WarpDrive works.


Change History:
V2 changed from V1:
1. Change kernel framework name from SPIMDEV (Share Parent IOMMU
   Mdev) to SDMDEV (Share Domain Mdev).
2. Allocate Hardware Resource when a new mdev is created (While
   it is allocated when the mdev is openned)
3. Unmap pages from the shared domain when the sdmdev iommu group is
   detached. (This procedure is necessary, but missed in V1)
4. Update document accordingly.
5. Rebase to the latest kernel (4.19.0-rc1)

According the review comment on RFCv1, We did try to use dma-buf
as back end of WarpDrive. It can work properly with the current
solution [4], but it cannot make use of process's
own memory address space directly. This is important to many
acceleration scenario. So dma-buf will be taken as a backup
alternative for noiommu scenario, it will be added in the future
version.


Refernces:
[1] https://www.spinics.net/lists/kernel/msg2651481.html
[2] https://github.com/Kenneth-Lee/linux-kernel-warpdrive/tree/warpdrive-sva-v0.5
[3] https://lkml.org/lkml/2018/7/22/34

Please refer to the latest version posted here for discussion.

https://lkml.org/lkml/2018/8/30/107

Sure. Thank you.

Best regards,
Lu Baolu

-- 
			-Kenneth(Hisilicon)

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