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Tsirkin" To: qemu-devel@nongnu.org Subject: [PULL v2 25/47] pcie: Add some SR/IOV API documentation in docs/pcie_sriov.txt Message-ID: <20220307100058.449628-26-mst@redhat.com> References: <20220307100058.449628-1-mst@redhat.com> MIME-Version: 1.0 In-Reply-To: <20220307100058.449628-1-mst@redhat.com> X-Mailer: git-send-email 2.27.0.106.g8ac3dc51b1 X-Mutt-Fcc: =sent Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=mst@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Disposition: inline Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Peter Maydell , Knut Omang , Knut Omang Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" From: Knut Omang Add a small intro + minimal documentation for how to implement SR/IOV support for an emulated device. Signed-off-by: Knut Omang Message-Id: <20220217174504.1051716-3-lukasz.maniak@linux.intel.com> Reviewed-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin --- docs/pcie_sriov.txt | 115 ++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 115 insertions(+) create mode 100644 docs/pcie_sriov.txt diff --git a/docs/pcie_sriov.txt b/docs/pcie_sriov.txt new file mode 100644 index 0000000000..f5e891e1d4 --- /dev/null +++ b/docs/pcie_sriov.txt @@ -0,0 +1,115 @@ +PCI SR/IOV EMULATION SUPPORT +============================ + +Description +=========== +SR/IOV (Single Root I/O Virtualization) is an optional extended capability +of a PCI Express device. It allows a single physical function (PF) to appear as multiple +virtual functions (VFs) for the main purpose of eliminating software +overhead in I/O from virtual machines. + +Qemu now implements the basic common functionality to enable an emulated device +to support SR/IOV. Yet no fully implemented devices exists in Qemu, but a +proof-of-concept hack of the Intel igb can be found here: + +git://github.com/knuto/qemu.git sriov_patches_v5 + +Implementation +============== +Implementing emulation of an SR/IOV capable device typically consists of +implementing support for two types of device classes; the "normal" physical device +(PF) and the virtual device (VF). From Qemu's perspective, the VFs are just +like other devices, except that some of their properties are derived from +the PF. + +A virtual function is different from a physical function in that the BAR +space for all VFs are defined by the BAR registers in the PFs SR/IOV +capability. All VFs have the same BARs and BAR sizes. + +Accesses to these virtual BARs then is computed as + + + * + + +From our emulation perspective this means that there is a separate call for +setting up a BAR for a VF. + +1) To enable SR/IOV support in the PF, it must be a PCI Express device so + you would need to add a PCI Express capability in the normal PCI + capability list. You might also want to add an ARI (Alternative + Routing-ID Interpretation) capability to indicate that your device + supports functions beyond it's "own" function space (0-7), + which is necessary to support more than 7 functions, or + if functions extends beyond offset 7 because they are placed at an + offset > 1 or have stride > 1. + + ... + #include "hw/pci/pcie.h" + #include "hw/pci/pcie_sriov.h" + + pci_your_pf_dev_realize( ... ) + { + ... + int ret = pcie_endpoint_cap_init(d, 0x70); + ... + pcie_ari_init(d, 0x100, 1); + ... + + /* Add and initialize the SR/IOV capability */ + pcie_sriov_pf_init(d, 0x200, "your_virtual_dev", + vf_devid, initial_vfs, total_vfs, + fun_offset, stride); + + /* Set up individual VF BARs (parameters as for normal BARs) */ + pcie_sriov_pf_init_vf_bar( ... ) + ... + } + + For cleanup, you simply call: + + pcie_sriov_pf_exit(device); + + which will delete all the virtual functions and associated resources. + +2) Similarly in the implementation of the virtual function, you need to + make it a PCI Express device and add a similar set of capabilities + except for the SR/IOV capability. Then you need to set up the VF BARs as + subregions of the PFs SR/IOV VF BARs by calling + pcie_sriov_vf_register_bar() instead of the normal pci_register_bar() call: + + pci_your_vf_dev_realize( ... ) + { + ... + int ret = pcie_endpoint_cap_init(d, 0x60); + ... + pcie_ari_init(d, 0x100, 1); + ... + memory_region_init(mr, ... ) + pcie_sriov_vf_register_bar(d, bar_nr, mr); + ... + } + +Testing on Linux guest +====================== +The easiest is if your device driver supports sysfs based SR/IOV +enabling. Support for this was added in kernel v.3.8, so not all drivers +support it yet. + +To enable 4 VFs for a device at 01:00.0: + + modprobe yourdriver + echo 4 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs + +You should now see 4 VFs with lspci. +To turn SR/IOV off again - the standard requires you to turn it off before you can enable +another VF count, and the emulation enforces this: + + echo 0 > /sys/bus/pci/devices/0000:01:00.0/sriov_numvfs + +Older drivers typically provide a max_vfs module parameter +to enable it at load time: + + modprobe yourdriver max_vfs=4 + +To disable the VFs again then, you simply have to unload the driver: + + rmmod yourdriver