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Wed, 05 Apr 2023 09:58:30 -0700 (PDT) X-Google-Smtp-Source: AKy350aff3Vn7GfMi9FGUufyWN3DeUImBzAR2ar/X3c8ZJ+hx//Iy0Yg29MGqzfdN+KPQzOvdsVFhg== X-Received: by 2002:a6b:5108:0:b0:75c:ef01:8d60 with SMTP id f8-20020a6b5108000000b0075cef018d60mr4556782iob.21.1680713910317; Wed, 05 Apr 2023 09:58:30 -0700 (PDT) Received: from redhat.com ([38.15.36.239]) by smtp.gmail.com with ESMTPSA id a22-20020a027356000000b004042607348dsm4029524jae.34.2023.04.05.09.58.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 05 Apr 2023 09:58:29 -0700 (PDT) Date: Wed, 5 Apr 2023 10:58:28 -0600 From: Alex Williamson To: "Liu, Yi L" Cc: "eric.auger@redhat.com" , "jgg@nvidia.com" , "Tian, Kevin" , "joro@8bytes.org" , "robin.murphy@arm.com" , "cohuck@redhat.com" , "nicolinc@nvidia.com" , "kvm@vger.kernel.org" , "mjrosato@linux.ibm.com" , "chao.p.peng@linux.intel.com" , "yi.y.sun@linux.intel.com" , "peterx@redhat.com" , "jasowang@redhat.com" , "shameerali.kolothum.thodi@huawei.com" , "lulu@redhat.com" , "suravee.suthikulpanit@amd.com" , "intel-gvt-dev@lists.freedesktop.org" , "intel-gfx@lists.freedesktop.org" , "linux-s390@vger.kernel.org" , "Hao, Xudong" , "Zhao, Yan Y" , "Xu, Terrence" , "Jiang, Yanting" Subject: Re: [PATCH v9 25/25] docs: vfio: Add vfio device cdev description Message-ID: <20230405105828.6d170cec.alex.williamson@redhat.com> In-Reply-To: References: <20230401151833.124749-1-yi.l.liu@intel.com> <20230401151833.124749-26-yi.l.liu@intel.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.35; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-s390@vger.kernel.org On Wed, 5 Apr 2023 14:00:00 +0000 "Liu, Yi L" wrote: > Hi Eric, > > > From: Eric Auger > > Sent: Wednesday, April 5, 2023 9:46 PM > > > > Hi Yi, > > > > On 4/1/23 17:18, Yi Liu wrote: > > > This gives notes for userspace applications on device cdev usage. > > > > > > Reviewed-by: Kevin Tian > > > Signed-off-by: Yi Liu > > > --- > > > Documentation/driver-api/vfio.rst | 132 ++++++++++++++++++++++++++++++ > > > 1 file changed, 132 insertions(+) > > > > > > diff --git a/Documentation/driver-api/vfio.rst b/Documentation/driver-api/vfio.rst > > > index 363e12c90b87..4f21be7bda8a 100644 > > > --- a/Documentation/driver-api/vfio.rst > > > +++ b/Documentation/driver-api/vfio.rst > > > @@ -239,6 +239,130 @@ group and can access them as follows:: > > > /* Gratuitous device reset and go... */ > > > ioctl(device, VFIO_DEVICE_RESET); > > > > > > +IOMMUFD and vfio_iommu_type1 > > > +---------------------------- > > > + > > > +IOMMUFD is the new user API to manage I/O page tables from userspace. > > > +It intends to be the portal of delivering advanced userspace DMA > > > +features (nested translation [5], PASID [6], etc.) while also providing > > > +a backwards compatibility interface for existing VFIO_TYPE1v2_IOMMU use > > > +cases. Eventually the vfio_iommu_type1 driver, as well as the legacy > > > +vfio container and group model is intended to be deprecated. > > > + > > > +The IOMMUFD backwards compatibility interface can be enabled two ways. > > > +In the first method, the kernel can be configured with > > > +CONFIG_IOMMUFD_VFIO_CONTAINER, in which case the IOMMUFD subsystem > > > +transparently provides the entire infrastructure for the VFIO > > > +container and IOMMU backend interfaces. The compatibility mode can > > > +also be accessed if the VFIO container interface, ie. /dev/vfio/vfio is > > > +simply symlink'd to /dev/iommu. Note that at the time of writing, the > > > +compatibility mode is not entirely feature complete relative to > > > +VFIO_TYPE1v2_IOMMU (ex. DMA mapping MMIO) and does not attempt to > > > +provide compatibility to the VFIO_SPAPR_TCE_IOMMU interface. Therefore > > > +it is not generally advisable at this time to switch from native VFIO > > > +implementations to the IOMMUFD compatibility interfaces. > > > + > > > +Long term, VFIO users should migrate to device access through the cdev > > > +interface described below, and native access through the IOMMUFD > > > +provided interfaces. > > > + > > > +VFIO Device cdev > > > +---------------- > > > + > > > +Traditionally user acquires a device fd via VFIO_GROUP_GET_DEVICE_FD > > > +in a VFIO group. > > > + > > > +With CONFIG_VFIO_DEVICE_CDEV=y the user can now acquire a device fd > > > +by directly opening a character device /dev/vfio/devices/vfioX where > > > +"X" is the number allocated uniquely by VFIO for registered devices. > > > +For noiommu devices, the character device would be named with "noiommu-" > > > +prefix. e.g. /dev/vfio/devices/noiommu-vfioX. > > > + > > > +The cdev only works with IOMMUFD. Both VFIO drivers and applications > > > +must adapt to the new cdev security model which requires using > > > +VFIO_DEVICE_BIND_IOMMUFD to claim DMA ownership before starting to > > > +actually use the device. Once BIND succeeds then a VFIO device can > > > +be fully accessed by the user. > > > + > > > +VFIO device cdev doesn't rely on VFIO group/container/iommu drivers. > > > +Hence those modules can be fully compiled out in an environment > > > +where no legacy VFIO application exists. > > > + > > > +So far SPAPR does not support IOMMUFD yet. So it cannot support device > > > +cdev neither. > > > + > > > +Device cdev Example > > > +------------------- > > > + > > > +Assume user wants to access PCI device 0000:6a:01.0:: > > > + > > > + $ ls /sys/bus/pci/devices/0000:6a:01.0/vfio-dev/ > > > + vfio0 > > > + > > > +This device is therefore represented as vfio0. The user can verify > > > +its existence:: > > > + > > > + $ ls -l /dev/vfio/devices/vfio0 > > > + crw------- 1 root root 511, 0 Feb 16 01:22 /dev/vfio/devices/vfio0 > > > + $ cat /sys/bus/pci/devices/0000:6a:01.0/vfio-dev/vfio0/dev > > you mentionned in the pci hot reset series that the BDF couldn't be used > > if cdev is being used. According to the above, it could, no? > > It should be the device passing case, otherwise, BDF can be used. But > from kernel p.o.v., it has no idea how user gets the device fd, so it needs > to assume user may not have BDF knowledge. > > > > + 511:0 > > > + $ ls -l /dev/char/511\:0 > > > + lrwxrwxrwx 1 root root 21 Feb 16 01:22 /dev/char/511:0 - > > > ../vfio/devices/vfio0 > > > + > > > +Then provide the user with access to the device if unprivileged > > > +operation is desired:: > > > + > > > + $ chown user:user /dev/vfio/devices/vfio0 > > > + > > > +Finally the user could get cdev fd by:: > > > + > > > + cdev_fd = open("/dev/vfio/devices/vfio0", O_RDWR); > > > + > > > +An opened cdev_fd doesn't give the user any permission of accessing > > > +the device except binding the cdev_fd to an iommufd. After that point > > > +then the device is fully accessible including attaching it to an > > > +IOMMUFD IOAS/HWPT to enable userspace DMA:: > > > + > > > + struct vfio_device_bind_iommufd bind = { > > > + .argsz = sizeof(bind), > > > + .flags = 0, > > > + }; > > > + struct iommu_ioas_alloc alloc_data = { > > > + .size = sizeof(alloc_data), > > > + .flags = 0, > > > + }; > > > + struct vfio_device_attach_iommufd_pt attach_data = { > > > + .argsz = sizeof(attach_data), > > > + .flags = 0, > > > + }; > > > + struct iommu_ioas_map map = { > > > + .size = sizeof(map), > > > + .flags = IOMMU_IOAS_MAP_READABLE | > > > + IOMMU_IOAS_MAP_WRITEABLE | > > > + IOMMU_IOAS_MAP_FIXED_IOVA, > > > + .__reserved = 0, > > > + }; > > > + > > > + iommufd = open("/dev/iommu", O_RDWR); > > > + > > > + bind.iommufd = iommufd; // negative value means vfio-noiommu mode > > > + ioctl(cdev_fd, VFIO_DEVICE_BIND_IOMMUFD, &bind); > > > + > > > + ioctl(iommufd, IOMMU_IOAS_ALLOC, &alloc_data); > > > + attach_data.pt_id = alloc_data.out_ioas_id; > > > + ioctl(cdev_fd, VFIO_DEVICE_ATTACH_IOMMUFD_PT, &attach_data); > > > + > > > + /* Allocate some space and setup a DMA mapping */ > > > + map.user_va = (int64_t)mmap(0, 1024 * 1024, PROT_READ | PROT_WRITE, > > > + MAP_PRIVATE | MAP_ANONYMOUS, 0, 0); > > > + map.iova = 0; /* 1MB starting at 0x0 from device view */ > > > + map.length = 1024 * 1024; > > > + map.ioas_id = alloc_data.out_ioas_id;; > > > + > > > + ioctl(iommufd, IOMMU_IOAS_MAP, &map); > > > + > > > + /* Other device operations as stated in "VFIO Usage Example" */ > > dev_id is not mentioned anywhere whereas it is used in the reset get > > info. Worth to be mentioned? > > a good point. but it is just for PCI devices, not sure if it is good to > mention it here. or the kdoc in the HOT_RESET_INFO ioctl is already > enough. Alex, how about your taste?. dev-id is just for PCI devices?? Maybe it's only a vfio-pci ioctl that's requiring it for input, but it's not a bus specific feature. There should be a description of how an iommufd property of the device maps to this subsystem. Thanks, Alex