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SubjectRe: [RFCv3 PATCH 1/6] uacce: Add documents for WarpDrive/uacce
On Mon, Nov 19, 2018 at 05:14:05PM +0800, Kenneth Lee wrote:
> Date: Mon, 19 Nov 2018 17:14:05 +0800
> From: Kenneth Lee <liguozhu@hisilicon.com>
> To: Leon Romanovsky <leon@kernel.org>
> CC: Tim Sell <timothy.sell@unisys.com>, linux-doc@vger.kernel.org,
> Alexander Shishkin <alexander.shishkin@linux.intel.com>, Zaibo Xu
> <xuzaibo@huawei.com>, zhangfei.gao@foxmail.com, linuxarm@huawei.com,
> haojian.zhuang@linaro.org, Christoph Lameter <cl@linux.com>, Hao Fang
> <fanghao11@huawei.com>, Gavin Schenk <g.schenk@eckelmann.de>, RDMA mailing
> list <linux-rdma@vger.kernel.org>, Vinod Koul <vkoul@kernel.org>, Jason
> Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>, Uwe
> Kleine-König <u.kleine-koenig@pengutronix.de>, David Kershner
> <david.kershner@unisys.com>, Kenneth Lee <nek.in.cn@gmail.com>, Johan
> Hovold <johan@kernel.org>, Cyrille Pitchen
> <cyrille.pitchen@free-electrons.com>, Sagar Dharia
> <sdharia@codeaurora.org>, Jens Axboe <axboe@kernel.dk>,
> guodong.xu@linaro.org, linux-netdev <netdev@vger.kernel.org>, Randy Dunlap
> <rdunlap@infradead.org>, linux-kernel@vger.kernel.org, Zhou Wang
> <wangzhou1@hisilicon.com>, linux-crypto@vger.kernel.org, Philippe
> Ombredanne <pombredanne@nexb.com>, Sanyog Kale <sanyog.r.kale@intel.com>,
> "David S. Miller" <davem@davemloft.net>,
> linux-accelerators@lists.ozlabs.org
> Subject: Re: [RFCv3 PATCH 1/6] uacce: Add documents for WarpDrive/uacce
> User-Agent: Mutt/1.5.21 (2010-09-15)
> Message-ID: <20181119091405.GE157308@Turing-Arch-b>
>
> On Thu, Nov 15, 2018 at 04:54:55PM +0200, Leon Romanovsky wrote:
> > Date: Thu, 15 Nov 2018 16:54:55 +0200
> > From: Leon Romanovsky <leon@kernel.org>
> > To: Kenneth Lee <liguozhu@hisilicon.com>
> > CC: Kenneth Lee <nek.in.cn@gmail.com>, Tim Sell <timothy.sell@unisys.com>,
> > linux-doc@vger.kernel.org, Alexander Shishkin
> > <alexander.shishkin@linux.intel.com>, Zaibo Xu <xuzaibo@huawei.com>,
> > zhangfei.gao@foxmail.com, linuxarm@huawei.com, haojian.zhuang@linaro.org,
> > Christoph Lameter <cl@linux.com>, Hao Fang <fanghao11@huawei.com>, Gavin
> > Schenk <g.schenk@eckelmann.de>, RDMA mailing list
> > <linux-rdma@vger.kernel.org>, Zhou Wang <wangzhou1@hisilicon.com>, Jason
> > Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>, Uwe
> > Kleine-König <u.kleine-koenig@pengutronix.de>, David Kershner
> > <david.kershner@unisys.com>, Johan Hovold <johan@kernel.org>, Cyrille
> > Pitchen <cyrille.pitchen@free-electrons.com>, Sagar Dharia
> > <sdharia@codeaurora.org>, Jens Axboe <axboe@kernel.dk>,
> > guodong.xu@linaro.org, linux-netdev <netdev@vger.kernel.org>, Randy Dunlap
> > <rdunlap@infradead.org>, linux-kernel@vger.kernel.org, Vinod Koul
> > <vkoul@kernel.org>, linux-crypto@vger.kernel.org, Philippe Ombredanne
> > <pombredanne@nexb.com>, Sanyog Kale <sanyog.r.kale@intel.com>, "David S.
> > Miller" <davem@davemloft.net>, linux-accelerators@lists.ozlabs.org
> > Subject: Re: [RFCv3 PATCH 1/6] uacce: Add documents for WarpDrive/uacce
> > User-Agent: Mutt/1.10.1 (2018-07-13)
> > Message-ID: <20181115145455.GN3759@mtr-leonro.mtl.com>
> >
> > On Thu, Nov 15, 2018 at 04:51:09PM +0800, Kenneth Lee wrote:
> > > On Wed, Nov 14, 2018 at 06:00:17PM +0200, Leon Romanovsky wrote:
> > > > Date: Wed, 14 Nov 2018 18:00:17 +0200
> > > > From: Leon Romanovsky <leon@kernel.org>
> > > > To: Kenneth Lee <nek.in.cn@gmail.com>
> > > > CC: Tim Sell <timothy.sell@unisys.com>, linux-doc@vger.kernel.org,
> > > > Alexander Shishkin <alexander.shishkin@linux.intel.com>, Zaibo Xu
> > > > <xuzaibo@huawei.com>, zhangfei.gao@foxmail.com, linuxarm@huawei.com,
> > > > haojian.zhuang@linaro.org, Christoph Lameter <cl@linux.com>, Hao Fang
> > > > <fanghao11@huawei.com>, Gavin Schenk <g.schenk@eckelmann.de>, RDMA mailing
> > > > list <linux-rdma@vger.kernel.org>, Zhou Wang <wangzhou1@hisilicon.com>,
> > > > Jason Gunthorpe <jgg@ziepe.ca>, Doug Ledford <dledford@redhat.com>, Uwe
> > > > Kleine-König <u.kleine-koenig@pengutronix.de>, David Kershner
> > > > <david.kershner@unisys.com>, Johan Hovold <johan@kernel.org>, Cyrille
> > > > Pitchen <cyrille.pitchen@free-electrons.com>, Sagar Dharia
> > > > <sdharia@codeaurora.org>, Jens Axboe <axboe@kernel.dk>,
> > > > guodong.xu@linaro.org, linux-netdev <netdev@vger.kernel.org>, Randy Dunlap
> > > > <rdunlap@infradead.org>, linux-kernel@vger.kernel.org, Vinod Koul
> > > > <vkoul@kernel.org>, linux-crypto@vger.kernel.org, Philippe Ombredanne
> > > > <pombredanne@nexb.com>, Sanyog Kale <sanyog.r.kale@intel.com>, Kenneth Lee
> > > > <liguozhu@hisilicon.com>, "David S. Miller" <davem@davemloft.net>,
> > > > linux-accelerators@lists.ozlabs.org
> > > > Subject: Re: [RFCv3 PATCH 1/6] uacce: Add documents for WarpDrive/uacce
> > > > User-Agent: Mutt/1.10.1 (2018-07-13)
> > > > Message-ID: <20181114160017.GI3759@mtr-leonro.mtl.com>
> > > >
> > > > On Wed, Nov 14, 2018 at 10:58:09AM +0800, Kenneth Lee wrote:
> > > > >
> > > > > 在 2018/11/13 上午8:23, Leon Romanovsky 写道:
> > > > > > On Mon, Nov 12, 2018 at 03:58:02PM +0800, Kenneth Lee wrote:
> > > > > > > From: Kenneth Lee <liguozhu@hisilicon.com>
> > > > > > >
> > > > > > > WarpDrive is a general accelerator framework for the user application to
> > > > > > > access the hardware without going through the kernel in data path.
> > > > > > >
> > > > > > > The kernel component to provide kernel facility to driver for expose the
> > > > > > > user interface is called uacce. It a short name for
> > > > > > > "Unified/User-space-access-intended Accelerator Framework".
> > > > > > >
> > > > > > > This patch add document to explain how it works.
> > > > > > + RDMA and netdev folks
> > > > > >
> > > > > > Sorry, to be late in the game, I don't see other patches, but from
> > > > > > the description below it seems like you are reinventing RDMA verbs
> > > > > > model. I have hard time to see the differences in the proposed
> > > > > > framework to already implemented in drivers/infiniband/* for the kernel
> > > > > > space and for the https://github.com/linux-rdma/rdma-core/ for the user
> > > > > > space parts.
> > > > >
> > > > > Thanks Leon,
> > > > >
> > > > > Yes, we tried to solve similar problem in RDMA. We also learned a lot from
> > > > > the exist code of RDMA. But we we have to make a new one because we cannot
> > > > > register accelerators such as AI operation, encryption or compression to the
> > > > > RDMA framework:)
> > > >
> > > > Assuming that you did everything right and still failed to use RDMA
> > > > framework, you was supposed to fix it and not to reinvent new exactly
> > > > same one. It is how we develop kernel, by reusing existing code.
> > >
> > > Yes, but we don't force other system such as NIC or GPU into RDMA, do we?
> >
> > You don't introduce new NIC or GPU, but proposing another interface to
> > directly access HW memory and bypass kernel for the data path. This is
> > whole idea of RDMA and this is why it is already present in the kernel.
> >
> > Various hardware devices are supported in our stack allow a ton of crazy
> > stuff, including GPUs interconnections and NIC functionalities.
>
> Yes. We don't want to invent new wheel. That is why we did it behind VFIO in RFC
> v1 and v2. But finally we were persuaded by Mr. Jerome Glisse that VFIO was not
> a good place to solve the problem.
>
> And currently, as you see, IB is bound with devices doing RDMA. The register
> function, ib_register_device() hint that it is a netdev (get_netdev() callback), it know
> about gid, pkey, and Memory Window. IB is not simply a address space management
> framework. And verbs to IB are not transparent. If we start to add
> compression/decompression, AI (RNN, CNN stuff) operations, and encryption/decryption
> to the verbs set. It will become very complexity. Or maybe I misunderstand the
> IB idea? But I don't see compression hardware is integrated in the mainline
> Kernel. Could you directly point out which one I can used as a reference?
>
> >
> > >
> > > I assume you would not agree to register a zip accelerator to infiniband? :)
> >
> > "infiniband" name in the "drivers/infiniband/" is legacy one and the
> > current code supports IB, RoCE, iWARP and OmniPath as a transport layers.
> > For a lone time, we wanted to rename that folder to be "drivers/rdma",
> > but didn't find enough brave men/women to do it, due to backport mess
> > for such move.
> >
> > The addition of zip accelerator to RDMA is possible and depends on how
> > you will model such new functionality - new driver, or maybe new ULP.
> >
> > >
> > > Further, I don't think it is wise to break an exist system (RDMA) to fulfill a
> > > totally new scenario. The better choice is to let them run in parallel for some
> > > time and try to merge them accordingly.
> >
> > Awesome, so please run your code out-of-tree for now and once you are ready
> > for submission let's try to merge it.
>
> Yes, yes. We know trust need time to gain. But the fact is that there is no
> accelerator user driver can be added to mainline kernel. We should raise the
> topic time to time. So to help the communication to fix the gap, right?
>
> We are also opened to cooperate with IB to do it within the IB framework. But
> please let me know where to start. I feel it is quite wired to make a
> ib_register_device for a zip or RSA accelerator.
>
> >
> > >
> > > >
> > > > >
> > > > > Another problem we tried to address is the way to pin the memory for dma
> > > > > operation. The RDMA way to pin the memory cannot avoid the page lost due to
> > > > > copy-on-write operation during the memory is used by the device. This may
> > > > > not be important to RDMA library. But it is important to accelerator.
> > > >
> > > > Such support exists in drivers/infiniband/ from late 2014 and
> > > > it is called ODP (on demand paging).
> > >
> > > I reviewed ODP and I think it is a solution bound to infiniband. It is part of
> > > MR semantics and required a infiniband specific hook
> > > (ucontext->invalidate_range()). And the hook requires the device to be able to
> > > stop using the page for a while for the copying. It is ok for infiniband
> > > (actually, only mlx5 uses it). I don't think most accelerators can support
> > > this mode. But WarpDrive works fully on top of IOMMU interface, it has no this
> > > limitation.
> >
> > 1. It has nothing to do with infiniband.
>
> But it must be a ib_dev first.
>
> > 2. MR and uncontext are verbs semantics and needed to ensure that host
> > memory exposed to user is properly protected from security point of view.
> > 3. "stop using the page for a while for the copying" - I'm not fully
> > understand this claim, maybe this article will help you to better
> > describe : https://lwn.net/Articles/753027/
>
> This topic was being discussed in RFCv2. The key problem here is that:
>
> The device need to hold the memory for its own calculation, but the CPU/software
> want to stop it for a while for synchronizing with disk or COW.
>
> If the hardware support SVM/SVA (Shared Virtual Memory/Address), it is easy, the
> device share page table with CPU, the device will raise a page fault when the
> CPU downgrade the PTE to read-only.
>
> If the hardware cannot share page table with the CPU, we then need to have
> some way to change the device page table. This is what happen in ODP. It
> invalidates the page table in device upon mmu_notifier call back. But this cannot
> solve the COW problem: if the user process A share a page P with device, and A
> forks a new process B, and it continue to write to the page. By COW, the
> process B will keep the page P, while A will get a new page P'. But you have
> no way to let the device know it should use P' rather than P.
>
> This may be OK for RDMA application. Because RDMA is a big thing and we can ask
> the programmer to avoid the situation. But for a accelerator, I don't think we
> can ask a programmer to care for this when use a zlib.
>
> In WarpDrive/uacce, we make this simple. If you support IOMMU and it support
> SVM/SVA. Everything will be fine just like ODP implicit mode. And you don't need
> to write any code for that. Because it has been done by IOMMU framework. If it
> dose not, you have to use the kernel allocated memory which has the same IOVA as
> the VA in user space. So we can still maintain a unify address space among the
> devices and the applicatin.
>
> > 4. mlx5 supports ODP not because of being partially IB device,
> > but because HW performance oriented implementation is not an easy task.
> >
> > >
> > > >
> > > > >
> > > > > Hope this can help the understanding.
> > > >
> > > > Yes, it helped me a lot.
> > > > Now, I'm more than before convinced that this whole patchset shouldn't
> > > > exist in the first place.
> > >
> > > Then maybe you can tell me how I can register my accelerator to the user space?
> >
> > Write kernel driver and write user space part of it.
> > https://github.com/linux-rdma/rdma-core/
> >
> > I have no doubts that your colleagues who wrote and maintain
> > drivers/infiniband/hw/hns driver know best how to do it.
> > They did it very successfully.
> >
> > Thanks
> >
> > >
> > > >
> > > > To be clear, NAK.
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > > Cheers
> > > > >
> > > > > >
> > > > > > Hard NAK from RDMA side.
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > > Signed-off-by: Kenneth Lee <liguozhu@hisilicon.com>
> > > > > > > ---
> > > > > > > Documentation/warpdrive/warpdrive.rst | 260 +++++++
> > > > > > > Documentation/warpdrive/wd-arch.svg | 764 ++++++++++++++++++++
> > > > > > > Documentation/warpdrive/wd.svg | 526 ++++++++++++++
> > > > > > > Documentation/warpdrive/wd_q_addr_space.svg | 359 +++++++++
> > > > > > > 4 files changed, 1909 insertions(+)
> > > > > > > create mode 100644 Documentation/warpdrive/warpdrive.rst
> > > > > > > create mode 100644 Documentation/warpdrive/wd-arch.svg
> > > > > > > create mode 100644 Documentation/warpdrive/wd.svg
> > > > > > > create mode 100644 Documentation/warpdrive/wd_q_addr_space.svg
> > > > > > >
> > > > > > > diff --git a/Documentation/warpdrive/warpdrive.rst b/Documentation/warpdrive/warpdrive.rst
> > > > > > > new file mode 100644
> > > > > > > index 000000000000..ef84d3a2d462
> > > > > > > --- /dev/null
> > > > > > > +++ b/Documentation/warpdrive/warpdrive.rst
> > > > > > > @@ -0,0 +1,260 @@
> > > > > > > +Introduction of WarpDrive
> > > > > > > +=========================
> > > > > > > +
> > > > > > > +*WarpDrive* is a general accelerator framework for the user application to
> > > > > > > +access the hardware without going through the kernel in data path.
> > > > > > > +
> > > > > > > +It can be used as the quick channel for accelerators, network adaptors or
> > > > > > > +other hardware for application in user space.
> > > > > > > +
> > > > > > > +This may make some implementation simpler. E.g. you can reuse most of the
> > > > > > > +*netdev* driver in kernel and just share some ring buffer to the user space
> > > > > > > +driver for *DPDK* [4] or *ODP* [5]. Or you can combine the RSA accelerator with
> > > > > > > +the *netdev* in the user space as a https reversed proxy, etc.
> > > > > > > +
> > > > > > > +*WarpDrive* takes the hardware accelerator as a heterogeneous processor which
> > > > > > > +can share particular load from the CPU:
> > > > > > > +
> > > > > > > +.. image:: wd.svg
> > > > > > > + :alt: WarpDrive Concept
> > > > > > > +
> > > > > > > +The virtual concept, queue, is used to manage the requests sent to the
> > > > > > > +accelerator. The application send requests to the queue by writing to some
> > > > > > > +particular address, while the hardware takes the requests directly from the
> > > > > > > +address and send feedback accordingly.
> > > > > > > +
> > > > > > > +The format of the queue may differ from hardware to hardware. But the
> > > > > > > +application need not to make any system call for the communication.
> > > > > > > +
> > > > > > > +*WarpDrive* tries to create a shared virtual address space for all involved
> > > > > > > +accelerators. Within this space, the requests sent to queue can refer to any
> > > > > > > +virtual address, which will be valid to the application and all involved
> > > > > > > +accelerators.
> > > > > > > +
> > > > > > > +The name *WarpDrive* is simply a cool and general name meaning the framework
> > > > > > > +makes the application faster. It includes general user library, kernel
> > > > > > > +management module and drivers for the hardware. In kernel, the management
> > > > > > > +module is called *uacce*, meaning "Unified/User-space-access-intended
> > > > > > > +Accelerator Framework".
> > > > > > > +
> > > > > > > +
> > > > > > > +How does it work
> > > > > > > +================
> > > > > > > +
> > > > > > > +*WarpDrive* uses *mmap* and *IOMMU* to play the trick.
> > > > > > > +
> > > > > > > +*Uacce* creates a chrdev for the device registered to it. A "queue" will be
> > > > > > > +created when the chrdev is opened. The application access the queue by mmap
> > > > > > > +different address region of the queue file.
> > > > > > > +
> > > > > > > +The following figure demonstrated the queue file address space:
> > > > > > > +
> > > > > > > +.. image:: wd_q_addr_space.svg
> > > > > > > + :alt: WarpDrive Queue Address Space
> > > > > > > +
> > > > > > > +The first region of the space, device region, is used for the application to
> > > > > > > +write request or read answer to or from the hardware.
> > > > > > > +
> > > > > > > +Normally, there can be three types of device regions mmio and memory regions.
> > > > > > > +It is recommended to use common memory for request/answer descriptors and use
> > > > > > > +the mmio space for device notification, such as doorbell. But of course, this
> > > > > > > +is all up to the interface designer.
> > > > > > > +
> > > > > > > +There can be two types of device memory regions, kernel-only and user-shared.
> > > > > > > +This will be explained in the "kernel APIs" section.
> > > > > > > +
> > > > > > > +The Static Share Virtual Memory region is necessary only when the device IOMMU
> > > > > > > +does not support "Share Virtual Memory". This will be explained after the
> > > > > > > +*IOMMU* idea.
> > > > > > > +
> > > > > > > +
> > > > > > > +Architecture
> > > > > > > +------------
> > > > > > > +
> > > > > > > +The full *WarpDrive* architecture is represented in the following class
> > > > > > > +diagram:
> > > > > > > +
> > > > > > > +.. image:: wd-arch.svg
> > > > > > > + :alt: WarpDrive Architecture
> > > > > > > +
> > > > > > > +
> > > > > > > +The user API
> > > > > > > +------------
> > > > > > > +
> > > > > > > +We adopt a polling style interface in the user space: ::
> > > > > > > +
> > > > > > > + int wd_request_queue(struct wd_queue *q);
> > > > > > > + void wd_release_queue(struct wd_queue *q);
> > > > > > > +
> > > > > > > + int wd_send(struct wd_queue *q, void *req);
> > > > > > > + int wd_recv(struct wd_queue *q, void **req);
> > > > > > > + int wd_recv_sync(struct wd_queue *q, void **req);
> > > > > > > + void wd_flush(struct wd_queue *q);
> > > > > > > +
> > > > > > > +wd_recv_sync() is a wrapper to its non-sync version. It will trapped into
> > > > > > > +kernel and waits until the queue become available.
> > > > > > > +
> > > > > > > +If the queue do not support SVA/SVM. The following helper function
> > > > > > > +can be used to create Static Virtual Share Memory: ::
> > > > > > > +
> > > > > > > + void *wd_preserve_share_memory(struct wd_queue *q, size_t size);
> > > > > > > +
> > > > > > > +The user API is not mandatory. It is simply a suggestion and hint what the
> > > > > > > +kernel interface is supposed to support.
> > > > > > > +
> > > > > > > +
> > > > > > > +The user driver
> > > > > > > +---------------
> > > > > > > +
> > > > > > > +The queue file mmap space will need a user driver to wrap the communication
> > > > > > > +protocol. *UACCE* provides some attributes in sysfs for the user driver to
> > > > > > > +match the right accelerator accordingly.
> > > > > > > +
> > > > > > > +The *UACCE* device attribute is under the following directory:
> > > > > > > +
> > > > > > > +/sys/class/uacce/<dev-name>/params
> > > > > > > +
> > > > > > > +The following attributes is supported:
> > > > > > > +
> > > > > > > +nr_queue_remained (ro)
> > > > > > > + number of queue remained
> > > > > > > +
> > > > > > > +api_version (ro)
> > > > > > > + a string to identify the queue mmap space format and its version
> > > > > > > +
> > > > > > > +device_attr (ro)
> > > > > > > + attributes of the device, see UACCE_DEV_xxx flag defined in uacce.h
> > > > > > > +
> > > > > > > +numa_node (ro)
> > > > > > > + id of numa node
> > > > > > > +
> > > > > > > +priority (rw)
> > > > > > > + Priority or the device, bigger is higher
> > > > > > > +
> > > > > > > +(This is not yet implemented in RFC version)
> > > > > > > +
> > > > > > > +
> > > > > > > +The kernel API
> > > > > > > +--------------
> > > > > > > +
> > > > > > > +The *uacce* kernel API is defined in uacce.h. If the hardware support SVM/SVA,
> > > > > > > +The driver need only the following API functions: ::
> > > > > > > +
> > > > > > > + int uacce_register(uacce);
> > > > > > > + void uacce_unregister(uacce);
> > > > > > > + void uacce_wake_up(q);
> > > > > > > +
> > > > > > > +*uacce_wake_up* is used to notify the process who epoll() on the queue file.
> > > > > > > +
> > > > > > > +According to the IOMMU capability, *uacce* categories the devices as follow:
> > > > > > > +
> > > > > > > +UACCE_DEV_NOIOMMU
> > > > > > > + The device has no IOMMU. The user process cannot use VA on the hardware
> > > > > > > + This mode is not recommended.
> > > > > > > +
> > > > > > > +UACCE_DEV_SVA (UACCE_DEV_PASID | UACCE_DEV_FAULT_FROM_DEV)
> > > > > > > + The device has IOMMU which can share the same page table with user
> > > > > > > + process
> > > > > > > +
> > > > > > > +UACCE_DEV_SHARE_DOMAIN
> > > > > > > + The device has IOMMU which has no multiple page table and device page
> > > > > > > + fault support
> > > > > > > +
> > > > > > > +If the device works in mode other than UACCE_DEV_NOIOMMU, *uacce* will set its
> > > > > > > +IOMMU to IOMMU_DOMAIN_UNMANAGED. So the driver must not use any kernel
> > > > > > > +DMA API but the following ones from *uacce* instead: ::
> > > > > > > +
> > > > > > > + uacce_dma_map(q, va, size, prot);
> > > > > > > + uacce_dma_unmap(q, va, size, prot);
> > > > > > > +
> > > > > > > +*uacce_dma_map/unmap* is valid only for UACCE_DEV_SVA device. It creates a
> > > > > > > +particular PASID and page table for the kernel in the IOMMU (Not yet
> > > > > > > +implemented in the RFC)
> > > > > > > +
> > > > > > > +For the UACCE_DEV_SHARE_DOMAIN device, uacce_dma_map/unmap is not valid.
> > > > > > > +*Uacce* call back start_queue only when the DUS and DKO region is mmapped. The
> > > > > > > +accelerator driver must use those dma buffer, via uacce_queue->qfrs[], on
> > > > > > > +start_queue call back. The size of the queue file region is defined by
> > > > > > > +uacce->ops->qf_pg_start[].
> > > > > > > +
> > > > > > > +We have to do it this way because most of current IOMMU cannot support the
> > > > > > > +kernel and user virtual address at the same time. So we have to let them both
> > > > > > > +share the same user virtual address space.
> > > > > > > +
> > > > > > > +If the device have to support kernel and user at the same time, both kernel
> > > > > > > +and the user should use these DMA API. This is not convenient. A better
> > > > > > > +solution is to change the future DMA/IOMMU design to let them separate the
> > > > > > > +address space between the user and kernel space. But it is not going to be in
> > > > > > > +a short time.
> > > > > > > +
> > > > > > > +
> > > > > > > +Multiple processes support
> > > > > > > +==========================
> > > > > > > +
> > > > > > > +In the latest mainline kernel (4.19) when this document is written, the IOMMU
> > > > > > > +subsystem do not support multiple process page tables yet.
> > > > > > > +
> > > > > > > +Most IOMMU hardware implementation support multi-process with the concept
> > > > > > > +of PASID. But they may use different name, e.g. it is call sub-stream-id in
> > > > > > > +SMMU of ARM. With PASID or similar design, multi page table can be added to
> > > > > > > +the IOMMU and referred by its PASID.
> > > > > > > +
> > > > > > > +*JPB* has a patchset to enable this[1]_. We have tested it with our hardware
> > > > > > > +(which is known as *D06*). It works well. *WarpDrive* rely on them to support
> > > > > > > +UACCE_DEV_SVA. If it is not enabled, *WarpDrive* can still work. But it
> > > > > > > +support only one process, the device will be set to UACCE_DEV_SHARE_DOMAIN
> > > > > > > +even it is set to UACCE_DEV_SVA initially.
> > > > > > > +
> > > > > > > +Static Share Virtual Memory is mainly used by UACCE_DEV_SHARE_DOMAIN device.
> > > > > > > +
> > > > > > > +
> > > > > > > +Legacy Mode Support
> > > > > > > +===================
> > > > > > > +For the hardware without IOMMU, WarpDrive can still work, the only problem is
> > > > > > > +VA cannot be used in the device. The driver should adopt another strategy for
> > > > > > > +the shared memory. It is only for testing, and not recommended.
> > > > > > > +
> > > > > > > +
> > > > > > > +The Folk Scenario
> > > > > > > +=================
> > > > > > > +For a process with allocated queues and shared memory, what happen if it forks
> > > > > > > +a child?
> > > > > > > +
> > > > > > > +The fd of the queue will be duplicated on folk, so the child can send request
> > > > > > > +to the same queue as its parent. But the requests which is sent from processes
> > > > > > > +except for the one who open the queue will be blocked.
> > > > > > > +
> > > > > > > +It is recommended to add O_CLOEXEC to the queue file.
> > > > > > > +
> > > > > > > +The queue mmap space has a VM_DONTCOPY in its VMA. So the child will lost all
> > > > > > > +those VMAs.
> > > > > > > +
> > > > > > > +This is why *WarpDrive* does not adopt the mode used in *VFIO* and *InfiniBand*.
> > > > > > > +Both solutions can set any user pointer for hardware sharing. But they cannot
> > > > > > > +support fork when the dma is in process. Or the "Copy-On-Write" procedure will
> > > > > > > +make the parent process lost its physical pages.
> > > > > > > +
> > > > > > > +
> > > > > > > +The Sample Code
> > > > > > > +===============
> > > > > > > +There is a sample user land implementation with a simple driver for Hisilicon
> > > > > > > +Hi1620 ZIP Accelerator.
> > > > > > > +
> > > > > > > +To test, do the following in samples/warpdrive (for the case of PC host): ::
> > > > > > > + ./autogen.sh
> > > > > > > + ./conf.sh # or simply ./configure if you build on target system
> > > > > > > + make
> > > > > > > +
> > > > > > > +Then you can get test_hisi_zip in the test subdirectory. Copy it to the target
> > > > > > > +system and make sure the hisi_zip driver is enabled (the major and minor of
> > > > > > > +the uacce chrdev can be gotten from the dmesg or sysfs), and run: ::
> > > > > > > + mknod /dev/ua1 c <major> <minior>
> > > > > > > + test/test_hisi_zip -z < data > data.zip
> > > > > > > + test/test_hisi_zip -g < data > data.gzip
> > > > > > > +
> > > > > > > +
> > > > > > > +References
> > > > > > > +==========
> > > > > > > +.. [1] https://patchwork.kernel.org/patch/10394851/
> > > > > > > +
> > > > > > > +.. vim: tw=78
> > > [...]
> > > > > > > --
> > > > > > > 2.17.1
> > > > > > >

I don't know if Mr. Jerome Glisse in the list. I think I should cc him for my
respectation to his help on last RFC.

- Kenneth

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