From mboxrd@z Thu Jan 1 00:00:00 1970 From: Xu Zaibo Subject: Re: [PATCH v2 13/40] vfio: Add support for Shared Virtual Addressing Date: Thu, 6 Sep 2018 15:26:40 +0800 Message-ID: <5B90D6B0.300@huawei.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Jean-Philippe Brucker , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-acpi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org" Cc: Will Deacon , "okaya-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org" , "liguozhu-C8/M+/jPZTeaMJb+Lgu22Q@public.gmane.org" , fanghao11 , "ashok.raj-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "rfranz-YGCgFSpz5w/QT0dZR+AlfA@public.gmane.org" , "kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "rgummal-gjFFaj9aHVfQT0dZR+AlfA@public.gmane.org" , =?UTF-8?B?57Gz57Gz?= , "dwmw2-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org" , "ilias.apalodimas-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" , "alex.williamson-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , Robin Murphy , "christian.koenig-5C7GfCeVMHo@public.gmane.org" List-Id: devicetree@vger.kernel.org On 2018/9/5 19:02, Jean-Philippe Brucker wrote: > 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. > At present, It seems no other way existing while being compatible with current logic. Thank you. Thanks, Zaibo