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Wed, 29 Mar 2023 15:57:59 -0700 (PDT) X-Google-Smtp-Source: AKy350ZjB6g4MnZXnp6LQWyrzpWRTxnEwfNS5Oun74wPc/2VqhYS17fcaEn6qOIbdj9/uz/LN80VSA== X-Received: by 2002:a92:c688:0:b0:315:537e:4b18 with SMTP id o8-20020a92c688000000b00315537e4b18mr13545882ilg.32.1680130679216; Wed, 29 Mar 2023 15:57:59 -0700 (PDT) Received: from redhat.com ([38.15.36.239]) by smtp.gmail.com with ESMTPSA id x10-20020a92300a000000b0030c0dce44b1sm9466042ile.15.2023.03.29.15.57.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 29 Mar 2023 15:57:56 -0700 (PDT) Date: Wed, 29 Mar 2023 16:57:55 -0600 From: Alex Williamson To: Yi Liu Cc: jgg@nvidia.com, kevin.tian@intel.com, joro@8bytes.org, robin.murphy@arm.com, cohuck@redhat.com, eric.auger@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, xudong.hao@intel.com, yan.y.zhao@intel.com, terrence.xu@intel.com, yanting.jiang@intel.com Subject: Re: [PATCH v8 24/24] docs: vfio: Add vfio device cdev description Message-ID: <20230329165755.71b7beab.alex.williamson@redhat.com> In-Reply-To: <20230329164749.2778aa04.alex.williamson@redhat.com> References: <20230327094047.47215-1-yi.l.liu@intel.com> <20230327094047.47215-25-yi.l.liu@intel.com> <20230329164749.2778aa04.alex.williamson@redhat.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, 29 Mar 2023 16:47:49 -0600 Alex Williamson wrote: > On Mon, 27 Mar 2023 02:40:47 -0700 > 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 | 127 ++++++++++++++++++++++++++++++ > > 1 file changed, 127 insertions(+) > > > > diff --git a/Documentation/driver-api/vfio.rst b/Documentation/driver-api/vfio.rst > > index 363e12c90b87..77408788b98d 100644 > > --- a/Documentation/driver-api/vfio.rst > > +++ b/Documentation/driver-api/vfio.rst > > @@ -239,6 +239,125 @@ 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 being backward > > +compatible with the vfio_iommu_type1 driver. Eventually vfio_iommu_type1 > > +will be deprecated. > > "... 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." > > > + > > +With the backward compatibility, no change is required for legacy > > VFIO +drivers or applications to connect a VFIO device to IOMMUFD. > > + > > + When CONFIG_IOMMUFD_VFIO_CONTAINER=n, VFIO container still provides > > + /dev/vfio/vfio which connects to vfio_iommu_type1. To disable VFIO > > + container and vfio_iommu_type1, the administrator could symbol link > > + /dev/vfio/vfio to /dev/iommu to enable VFIO container emulation > > + in IOMMUFD. > > + > > + When CONFIG_IOMMUFD_VFIO_CONTAINER=y, IOMMUFD directly provides > > + /dev/vfio/vfio while the VFIO container and vfio_iommu_type1 are > > + explicitly disabled. > > + > > "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 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." > > Thanks, > Alex > > > +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 > > + 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); Even here the dev_cookie is nowhere to be found! Thanks, Alex > > + > > + 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" > > */ + > > VFIO User API > > ------------------------------------------------------------------------------- > > > > @@ -566,3 +685,11 @@ This implementation has some specifics: > > \-0d.1 > > > > 00:1e.0 PCI bridge: Intel Corporation 82801 PCI Bridge (rev > > 90) + > > +.. [5] Nested translation is an IOMMU feature which supports two > > stage > > + address translations. This improves the address translation > > efficiency > > + in IOMMU virtualization. > > + > > +.. [6] PASID stands for Process Address Space ID, introduced by PCI > > + Express. It is a prerequisite for Shared Virtual Addressing (SVA) > > + and Scalable I/O Virtualization (Scalable IOV). >