From mboxrd@z Thu Jan 1 00:00:00 1970 From: Zhu Lingshan Subject: Re: [PATCH] vhost: introduce vDPA based backend Date: Thu, 6 Feb 2020 11:21:27 +0800 Message-ID: <4b1753eb-b281-17e0-6636-849ac20cbe50@linux.intel.com> References: <20200131033651.103534-1-tiwei.bie@intel.com> <7aab2892-bb19-a06a-a6d3-9c28bc4c3400@redhat.com> <20200205020247.GA368700@___> <112858a4-1a01-f4d7-e41a-1afaaa1cad45@redhat.com> <20200205125648.GV23346@mellanox.com> <20200205081210-mutt-send-email-mst@kernel.org> <55b050d6-b31d-f8a2-2a15-0fc68896d47f@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <55b050d6-b31d-f8a2-2a15-0fc68896d47f@redhat.com> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Jason Wang , "Michael S. Tsirkin" , Jason Gunthorpe Cc: Shahaf Shuler , Tiwei Bie , "linux-kernel@vger.kernel.org" , "kvm@vger.kernel.org" , "virtualization@lists.linux-foundation.org" , "netdev@vger.kernel.org" , "rob.miller@broadcom.com" , "haotian.wang@sifive.com" , "eperezma@redhat.com" , "lulu@redhat.com" , Parav Pandit , "rdunlap@infradead.org" , "hch@infradead.org" , Jiri Pirko , "hanand@xilinx.com" , "mhabets@solarflare.com" ma List-Id: virtualization@lists.linuxfoundation.org On 2/6/2020 11:11 AM, Jason Wang wrote: > > On 2020/2/5 下午9:14, Michael S. Tsirkin wrote: >> On Wed, Feb 05, 2020 at 08:56:48AM -0400, Jason Gunthorpe wrote: >>> On Wed, Feb 05, 2020 at 03:50:14PM +0800, Jason Wang wrote: >>>>> Would it be better for the map/umnap logic to happen inside each >>>>> device ? >>>>> Devices that needs the IOMMU will call iommu APIs from inside the >>>>> driver callback. >>>> Technically, this can work. But if it can be done by vhost-vpda it >>>> will make >>>> the vDPA driver more compact and easier to be implemented. >>> Generally speaking, in the kernel, it is normal to not hoist code of >>> out drivers into subsystems until 2-3 drivers are duplicating that >>> code. It helps ensure the right design is used >>> >>> Jason >> That's up to the sybsystem maintainer really, as there's also some >> intuition involved in guessing a specific API is widely useful. >> In-kernel APIs are flexible, if we find something isn't needed we just >> drop it. >> > > If I understand correctly. At least Intel (Ling Shan) and Brodcom > (Rob) doesn't want to deal with DMA stuffs in their driver. > > Anyway since the DMA bus operations is optional, driver may still > choose to do DMA by itself if they want even if it requires platform > IOMMU to work. > > Thanks > Many Thanks if this could be done. The parent device has DMA capabilities and dma ops implemented, we hope can make use of it, as discussed in the vdpa thread.