From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Subject: Re: [PATCH v2 13/40] vfio: Add support for Shared Virtual Addressing To: Xu Zaibo , "linux-arm-kernel@lists.infradead.org" , "linux-pci@vger.kernel.org" , "linux-acpi@vger.kernel.org" , "devicetree@vger.kernel.org" , "iommu@lists.linux-foundation.org" , "kvm@vger.kernel.org" , "linux-mm@kvack.org" Cc: "joro@8bytes.org" , Will Deacon , Robin Murphy , "alex.williamson@redhat.com" , "tn@semihalf.com" , "thunder.leizhen@huawei.com" , "ilias.apalodimas@linaro.org" , "jonathan.cameron@huawei.com" , "liudongdong3@huawei.com" , "shunyong.yang@hxt-semitech.com" , "nwatters@codeaurora.org" , "okaya@codeaurora.org" , "jcrouse@codeaurora.org" , "rfranz@cavium.com" , "dwmw2@infradead.org" , "jacob.jun.pan@linux.intel.com" , "yi.l.liu@intel.com" , "ashok.raj@intel.com" , "kevin.tian@intel.com" , "baolu.lu@linux.intel.com" , "robdclark@gmail.com" , "christian.koenig@amd.com" , "bharatku@xilinx.com" , "rgummal@xilinx.com" , =?UTF-8?B?57Gz57Gz?= , wangzhou1 , "liguozhu@hisilicon.com" , fanghao11 References: <20180511190641.23008-1-jean-philippe.brucker@arm.com> <20180511190641.23008-14-jean-philippe.brucker@arm.com> <5B83B11E.7010807@huawei.com> <1d5b6529-4e5a-723c-3f1b-dd5a9adb490c@arm.com> <5B89F818.7060300@huawei.com> <3a961aff-e830-64bb-b6a9-14e08de1abf5@arm.com> <5B8DEA15.7020404@huawei.com> <5B8F4A59.20004@huawei.com> From: Jean-Philippe Brucker Message-ID: Date: Wed, 5 Sep 2018 12:02:29 +0100 MIME-Version: 1.0 In-Reply-To: <5B8F4A59.20004@huawei.com> Content-Type: text/plain; charset=utf-8 Sender: linux-acpi-owner@vger.kernel.org List-ID: On 05/09/2018 04:15, Xu Zaibo wrote: >>> 1. While the series are finished well, VFIO-PCI device can be held >>> by only one process >>> through binding IOCTL command without PASID (without PASID >>> being exposed user space). >> It could, but isn't supported at the moment. In addition to adding >> support in the I/O page fault code, we'd also need to update the VFIO >> API. Currently a VFIO_TYPE1 domain always supports the MAP/UNMAP ioctl. >> The case you describe isn't compatible with MAP/UNMAP, since the process >> manages the shared address space with mmap or malloc. We'd probably need >> to introduce a new VFIO IOMMU type, in which case the bind could be >> performed implicitly when the process does VFIO_SET_IOMMU. Then the >> process wouldn't need to send an additional BIND IOCTL. > ok. got it. This is the legacy mode, so all the VFIO APIs are kept > unchanged? Yes, existing VFIO semantics are preserved >>> 2. While using VFIO-PCI device to support multiple processes with >>> SVA series, a primary >>> process with multiple secondary processes must be deployed just >>> like DPDK(https://www.dpdk.org/). >>> And, the PASID still has to be exposed to user land. >> Right. A third case, also implemented by this patch (and complete), is >> the primary process simply doing a BIND for itself, and using the >> returned PASID to share its own address space with the device. >> > ok. But I am worried that the sulotion of one primary processes with > several secondary ones > > is a little bit limited. Maybe, users don't want to depend on the > primary process. :) I don't see a better way for vfio-pci, though. But more importantly, I don't know of any users :) While the feature is great for testing new hardware, and I've been using it for all kinds of stress testing, I haven't received feedback from possible users in production settings (DPDK etc) and can't speculate about what they'd prefer. Thanks, Jean