Stratos-dev June 2022

stratos-dev@op-lists.linaro.org

6 participants
5 discussions

Solution to restrict memory access under Xen

by Mathieu Poirier

Hi all, I came across this work [1] from Oleksandr today while shuffling through patches on LKML. I haven't looked at the details but from the cover letter is seems to provide the same kind of functionality as P-KVM. I will monitor the progress of this patchset. Regards, Mathieu [1]. https://www.spinics.net/lists/arm-kernel/msg970906.html

3 years

Next VirtIO device for Project Stratos?

by Alex Bennée

Hi, This email is driven by a brain storming session at a recent sprint where we considered what VirtIO devices we should look at implementing next. I ended up going through all the assigned device IDs hunting for missing spec discussion and existing drivers so I'd welcome feedback from anybody actively using them - especially as my suppositions about device types I'm not familiar with may be way off! Work so far =========== The devices we've tackled so far have been relatively simple ones and more focused on the embedded workloads. Both the i2c and gpio virtio devices allow for a fairly simple backend which can multiplex multiple client VM requests onto a set of real HW presented via the host OS. We have also done some work on a vhost-user backend for virtio-video and have a working PoC although it is a couple of iterations behind the latest submission to the virtio spec. Continuing work on this is currently paused while Peter works on libcamera related things (although more on that later). Upstream first ============== We've been pretty clear about the need to do things in an upstream compatible way which means devices should be: - properly specified in the OASIS spec - have at least one driver up-streamed (probably in Linux) - have a working public backend for Stratos I think we are pretty happy to implement all new backends in Rust under the auspices of the rust-vmm project and the vhost-device repository. We obviously also need a reasonable use case for why abstracting a HW type is useful. For example i2c was envisioned as useful on mobile devices where a lot of disparate auxillary HW is often hanging of an i2c bus. Current reserved IDs ==================== Looking at the spec there are currently 42 listed device types in the reserved ID table. While there are quite a lot that have Linux driver implementations a number are nothing more than reserved numbers: ioMemory / 6 ------------ No idea what this was meant to be. rpmsg / 7 --------- Not formalised in the specification but there is a driver in the Linux kernel. AFAIUI I think it's a fairly simple wrapper around the existing rpmsg bus. I think this has also been used for OpenAMP's hypervisor-less VirtIO experiments to communicate between processor domains. mac80211 wlan / 10 mac80211 hwsim wireless simulation device / 29 ---------------------------------------------- When the discussion about a virtio-wifi come up there is inevitably a debate about what the use case is. There are usually two potential use cases: - simulation environment Here the desire is to have something that looks like a real WiFi device in simulation so the rest of the stack (up from the driver) can be the same as when running on real HW. - abstraction environment Devices with WiFi are different from fixed networking as they need to deal with portability events like changing networks and reporting connection status and quality. If the guest VM is responsible for the UI it needs to gather this information and generally wants it's userspace components to use the same kernel APIs to get it as it would with real HW. Neither of these have up-streamed the specification to OASIS but there is an implementation of the mac80211_hwsim in the Linux kernel. I found evidence of a plain 80211 virtio_wifi.c existing in the Android kernel trees. So far I've been unable to find backends for these devices but I assume they must exist if the drivers do! Debates about what sort of features and control channels need to be supported often run into questions about why existing specifications can't be expanded (for example expand virtio-net with a control channel to report additional wifi related metadata) or use pass through sockets for talking to the host netlink channel. rproc serial / 11 ----------------- Again this isn't documented in the standard. I'm not sure if this is related to rpmsg but there is an implementation as part of the kernel virtio_console code. virtio CAIF / 12 ---------------- Not documented in the specification although there is a driver in the kernel as part of the orphaned CAIF networking subsystem. From the kernel documentation this was a sub-system for talking to modem parts. memory balloon / 13 ------------------- This seems like an abandoned attempt at a next generation version of the memory ballooning interface. Timer/Clock device / 17 ----------------------- This looks like a simple reservation with no proposed implementation. I don't know if there is a case for this on most modern architectures which usually have virtualised architected timers anyway. Access to RTC information may be something that mediated by firmware/system control buses. For emulation there are a fair number of industry standard RTC chips modelled and RTC access tends not to be performance critical. Signal Distribution Module / 21 ------------------------------- This appears to be a intra-domain communication channel for which an RFC was posted: https://lists.oasis-open.org/archives/virtio-dev/201606/msg00030.html it came with references to kernel and QEMU implementations. I don't know if this approach has been obviated by other communcation channels like vsock or scmi. pstore device / 22 ------------------ This appears to be a persistent storage device that was intended to allow guests to dump information like crash dumps. There was a proposed kernel driver: https://lwn.net/Articles/698744/ and a proposed QEMU backend: https://lore.kernel.org/all/1469632111-23260-1-git-send-email-namhyung@kern… which were never merged. As far as I can tell no proposal for the virtio spec itself. Video encoder device / 30 Video decoder device / 31 ------------------------- This is an ongoing development which has iterated several versions of the spec and the kernel side driver. NitroSecureModule / 33 ---------------------- This is a stripped down Trusted Platform Module (TPM) intended to expose TPM functionality such as cryptographic functions and attestation to guests. This looks like it is closely tied with AWS's Nitro Enclaves. I haven't been able to find any public definition of the spec or implementation details. How would this interact with other TPM functionality solutions? Watchdog / 35 ------------- Discussion about this is usually conflated with reset functionality as the two are intimately related. An early interest in this was for providing a well specified reset functionality firmware running on the -M virt machine model in QEMU. The need has been reduced somewhat with the provision of the sbsa-ref model which does have a defined reset pin. Other questions that would need to be answered include how the functionality would interact with the hypervisor given a vCPU could easily not be scheduled by it and therefore miss its kick window. Currently there have been no proposals for the spec or implementations. CAN / 36 -------- This is a device of interest to the Automotive industry as it looks to consolidate numerous ECUs into VM based work loads. There was a proposed RFC last year: https://markmail.org/message/hdxj35fsthypllkt?q=virtio-can+list:org%2Eoasis… and it is presumed there are frontend and backend drivers in vendor trees. At the last AGL virtualization expert meeting the Open Synergy guys said they hoped to post new versions of the spec and kernel driver soon: https://confluence.automotivelinux.org/pages/viewpage.action?spaceKey=VE&ti… During our discussion it became clear that while the message bus itself was fairly simple real HW often has a vendor specific control plane to enable specific features. Being able to present this flexibility via the virtio interface without baking in a direct mapping of the HW would be the challenge. Parameter Server / 38 --------------------- This is a proposal for a key-value parameter store over virtio. The exact use case is unclear but I suspect for Arm at least there is overlap with what is already supported by DT and UEFI variables. The proposal only seems to have been partially archived on the lists: https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg07201.html It may be Android related? Audio policy device / 39 ------------------------ Again I think this stems from the Android world and provides a policy and control device to work in concert with the virtio-sound device. The initial proposal to the list is here: https://www.mail-archive.com/virtio-dev@lists.oasis-open.org/msg07255.html The idea seems to be to have a control layer for dealing with routing and priority of multiple audio streams. Bluetooth device / 40 --------------------- Bluetooth suffers from similar complexity problems as 802.11 WiFi. However the virtio_bt driver in the kernel concentrates on providing a pipe for a standardised Host Control Interface (HCI) albeit with support for a selection of vendor specific commands. I could not find any submission of the specification for standarisation. Specified but missing backends? =============================== GPU device / 16 --------------- This is now a fairly mature part of the spec and has implementations is the kernel, QEMU and a vhost-user backend. However as is commensurate with the complexity of GPUs there is ongoing development moving from the VirGL OpenGL encapsulation to a thing called GFXSTREAM which is meant to make some things easier. A potential area of interest here is working out what the differences are in use cases between virtio-gpu and virtio-wayland. virtio-wayland is currently a ChromeOS only invention so hasn't seen any upstreaming or specification work but may make more sense where multiple VMs are drawing only elements of a final display which is composited by a master program. For further reading see Alyssa's write-up: https://alyssa.is/using-virtio-wl/ I'm not sure how widely used the existing vhost-user backend is for virtio-gpu but it could present an opportunity for a more beefy rust-vmm backend implementation? Audio device / 25 ----------------- This has a specification and a working kernel driver. However there isn't a working backend for QEMU although one has been proposed: Subject: [RFC PATCH 00/27] Virtio sound card implementation Date: Thu, 29 Apr 2021 17:34:18 +0530 Message-Id: <20210429120445.694420-1-chouhan.shreyansh2702(a)gmail.com> this could be a candidate for a rust-vmm version? Other suggestions ================= When we started Project Stratos there was a survey amongst members on where there was interest. virtio-spi/virtio-greybus ------------------------- Yet another serial bus. We chose to do i2c but doing another similar bus wouldn't be pushing the state of the art. We could certainly mentor/guide someone else who wants to get involved in rust-vmm though. virtio-tuner/virtio-radio ------------------------- These were early automotive requests. I don't know where these would sit in relation to the existing virtio-sound and audio policy devices. virtio-camera ------------- We have a prototype of virtio-video but as the libcamera project shows interfacing with modern cameras is quite a complex task these days. Modern cameras have all sorts of features powered by complex IP blocks including various amounts of AI. Perhaps it makes more sense to leave this to see how the libcamera project progresses before seeing what common features could be exposed. Conclusion ========== Considering the progress we've made so far and our growing confidence with rust-vmm I think the next device we implement a backend for should be a more complex device. Discussing this with Viresh and Mathieu earlier today we thought it would be nice if the device was more demo friendly as CLI's don't often excite. My initial thoughts is that a rust-vmm backend for virtio-gpu would fit the bill because: - already up-streamed in specification and kernel - known working implementations in QEMU and C based vhost-user daemon - ongoing development would be a good test of Rust's flexibility I think virtio-can would also be a useful target for the automotive use case. Given there will be a new release of the spec soon we should certainly keep an eye on it. Anyway I welcome peoples thoughts. -- Alex Bennée See also: Remaining Xen enabling work for rust-vmm - 87pmk472ii.fsf(a)linaro.org vhost-device outstanding tasks - 87zgj87alq.fsf(a)linaro.org

3 years, 1 month

Re: Understanding osdep_xenforeignmemory_map mmap behaviour

by Stefano Stabellini

I am pretty sure the reasons have to do with old x86 PV guests, so I am CCing Juergen and Boris. > Hi, > > While we've been working on the rust-vmm virtio backends on Xen we > obviously have to map guest memory info the userspace of the daemon. > However following the logic of what is going on is a little confusing. > For example in the Linux backend we have this: > > void *osdep_xenforeignmemory_map(xenforeignmemory_handle *fmem, > uint32_t dom, void *addr, > int prot, int flags, size_t num, > const xen_pfn_t arr[/*num*/], int err[/*num*/]) > { > int fd = fmem->fd; > privcmd_mmapbatch_v2_t ioctlx; > size_t i; > int rc; > > addr = mmap(addr, num << XC_PAGE_SHIFT, prot, flags | MAP_SHARED, > fd, 0); > if ( addr == MAP_FAILED ) > return NULL; > > ioctlx.num = num; > ioctlx.dom = dom; > ioctlx.addr = (unsigned long)addr; > ioctlx.arr = arr; > ioctlx.err = err; > > rc = ioctl(fd, IOCTL_PRIVCMD_MMAPBATCH_V2, &ioctlx); > > Where the fd passed down is associated with the /dev/xen/privcmd device > for issuing hypercalls on userspaces behalf. What is confusing is why > the function does it's own mmap - one would assume the passed addr would > be associated with a anonymous or file backed mmap region already that > the calling code has setup. Applying a mmap to a special device seems a > little odd. > > Looking at the implementation on the kernel side it seems the mmap > handler only sets a few flags: > > static int privcmd_mmap(struct file *file, struct vm_area_struct *vma) > { > /* DONTCOPY is essential for Xen because copy_page_range doesn't know > * how to recreate these mappings */ > vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTCOPY | > VM_DONTEXPAND | VM_DONTDUMP; > vma->vm_ops = &privcmd_vm_ops; > vma->vm_private_data = NULL; > > return 0; > } > > So can I confirm that the mmap of /dev/xen/privcmd is being called for > side effects? Is it so when the actual ioctl is called the correct flags > are set of the pages associated with the user space virtual address > range? > > Can I confirm there shouldn't be any limitation on where and how the > userspace virtual address space is setup for the mapping in the guest > memory? > > Is there a reason why this isn't done in the ioctl path itself? > > I'm trying to understand the differences between Xen and KVM in the API > choices here. I think the equivalent is the KVM_SET_USER_MEMORY_REGION > ioctl for KVM which brings a section of the guest physical address space > into the userspaces vaddr range.

3 years, 1 month

Virtio on Xen with Rust

by Viresh Kumar

Hello, We verified our hypervisor-agnostic Rust based vhost-user backends with Qemu based setup earlier, and there was growing concern if they were truly hypervisor-agnostic. In order to prove that, we decided to give it a try with Xen, a type-1 bare-metal hypervisor. We are happy to announce that we were able to make progress on that front and have a working setup where we can test our existing Rust based backends, like I2C, GPIO, RNG (though only I2C is tested as of now) over Xen. Key components: -------------- - Xen: https://github.com/vireshk/xen Xen requires MMIO and device specific support in order to populate the required devices at the guest. This tree contains four patches on the top of mainline Xen, two from Oleksandr (mmio/disk) and two from me (I2C). - libxen-sys: https://github.com/vireshk/libxen-sys We currently depend on the userspace tools/libraries provided by Xen, like xendevicemodel, xenevtchn, xenforeignmemory, etc. This crates provides Rust wrappers over those calls, generated automatically with help of bindgen utility in Rust, that allow us to use the installed Xen libraries. Though we plan to replace this with Rust based "oxerun" (find below) in longer run. - oxerun (WIP): https://gitlab.com/mathieupoirier/oxerun/-/tree/xen-ioctls This is Rust based implementations for Ioctl and hypercalls to Xen. This is WIP and should eventually replace "libxen-sys" crate entirely (which are C based implementation of the same). - vhost-device: https://github.com/vireshk/vhost-device These are Rust based vhost-user backends, maintained inside the rust-vmm project. This already contain support for I2C and RNG, while GPIO is under review. These are not required to be modified based on hypervisor and are truly hypervisor-agnostic. Ideally the backends are hypervisor agnostic, as explained earlier, but because of the way Xen maps the guest memory currently, we need a minor update for the backends to work. Xen maps the memory via a kernel file /dev/xen/privcmd, which needs calls to mmap() followed by an ioctl() to make it work. For this a hack has been added to one of the rust-vmm crates, vm-virtio, which is used by vhost-user. https://github.com/vireshk/vm-memory/commit/54b56c4dd7293428edbd7731c4dbe57… The update to vm-memory is responsible to do ioctl() after the already present mmap(). - vhost-user-master (WIP): https://github.com/vireshk/vhost-user-master This implements the master side interface of the vhost protocol, and is like the vhost-user-backend (https://github.com/rust-vmm/vhost-user-backend) crate maintained inside the rust-vmm project, which provides similar infrastructure for the backends to use. This shall be hypervisor independent and provide APIs for the hypervisor specific implementations. This will eventually be maintained inside the rust-vmm project and used by all Rust based hypervisors. - xen-vhost-master (WIP): https://github.com/vireshk/xen-vhost-master This is the Xen specific implementation and uses the APIs provided by "vhost-user-master", "oxerun" and "libxen-sys" crates for its functioning. This is designed based on the EPAM's "virtio-disk" repository (https://github.com/xen-troops/virtio-disk/) and is pretty much similar to it. One can see the analogy as: Virtio-disk == "Xen-vhost-master" + "vhost-user-master" + "oxerun" + "libxen-sys" + "vhost-device". Test setup: ---------- 1. Build Xen: $ ./configure --libdir=/usr/lib --build=x86_64-unknown-linux-gnu --host=aarch64-linux-gnu --disable-docs --disable-golang --disable-ocamltools --with-system-qemu=/root/qemu/build/i386-softmmu/qemu-system-i386; $ make -j9 debball CROSS_COMPILE=aarch64-linux-gnu- XEN_TARGET_ARCH=arm64 2. Run Xen via Qemu on X86 machine: $ qemu-system-aarch64 -machine virt,virtualization=on -cpu cortex-a57 -serial mon:stdio \ -device virtio-net-pci,netdev=net0 -netdev user,id=net0,hostfwd=tcp::8022-:22 \ -device virtio-scsi-pci -drive file=/home/vireshk/virtio/debian-bullseye-arm64.qcow2,index=0,id=hd0,if=none,format=qcow2 -device scsi-hd,drive=hd0 \ -display none -m 8192 -smp 8 -kernel /home/vireshk/virtio/xen/xen \ -append "dom0_mem=5G,max:5G dom0_max_vcpus=7 loglvl=all guest_loglvl=all" \ -device guest-loader,addr=0x46000000,kernel=/home/vireshk/kernel/barm64/arch/arm64/boot/Image,bootargs="root=/dev/sda2 console=hvc0 earlyprintk=xen" \ -device ds1338,address=0x20 # This is required to create a virtual I2C based RTC device on Dom0. This should get Dom0 up and running. 3. Build rust crates: $ cd /root/ $ git clone https://github.com/vireshk/xen-vhost-master $ cd xen-vhost-master $ cargo build $ cd ../ $ git clone https://github.com/vireshk/vhost-device $ cd vhost-device $ cargo build 4. Setup I2C based RTC device $ echo ds1338 0x20 > /sys/bus/i2c/devices/i2c-0/new_device; echo 0-0020 > /sys/bus/i2c/devices/0-0020/driver/unbind 5. Lets run everything now # Start the I2C backend in one terminal (open new terminal with "ssh # root@localhost -p8022"). This tells the I2C backend to hook up to # "/root/vi2c.sock0" socket and wait for the master to start transacting. $ /root/vhost-device/target/debug/vhost-device-i2c -s /root/vi2c.sock -c 1 -l 0:32 # Start the xen-vhost-master in another terminal. This provides the path of # the socket to the master side and the device to look from Xen, which is I2C # here. $ /root/xen-vhost-master/target/debug/xen-vhost-master --socket-path /root/vi2c.sock0 --name i2c # Start guest in another terminal, i2c_domu.conf is attached. The guest kernel # should have Virtio related config options enabled, along with i2c-virtio # driver. $ xl create -c i2c_domu.conf # The guest should boot fine now. Once the guest is up, you can create the I2C # RTC device and use it. Following will create /dev/rtc0 in the guest, which # you can configure with 'hwclock' utility. $ echo ds1338 0x20 > /sys/bus/i2c/devices/i2c-0/new_device Hope this helps. -- viresh

3 years, 3 months

virtio-media-source for cloud native workloads?

by Alex Bennée

Hi, In my last survey of assigned device numbers I went through all the currently assigned device numbers and attempted to glean their current status. However we currently don't have any devices that might be useful in a Cloud Native development environment. To define terms cloud native is the idea you can build a workload processing element as a VM and run it in the cloud. It consumes data from virtio-devices and processes it in someway. This VM can then be moved from being hosted in the cloud and into a real platform which still provides it's data via a virtio device. The idea being you get the same behaviour (as well as allowing for data to be recorded so future debugging/tuning work can be done in the cloud). Currently most of the virtio devices are actually data sinks - for example for virtio-video the guest pushes data to the video device for it to process. What we need is a device(s?) to be a source of data to feed to these workloads. Why virtio-media-source? Well rather than creating a device for every data type maybe it would make more sense to have a generic device which can advertise the data stream info in it's configuration space. This would allow the kernel driver to then route the data to the appropriate kernel subsystem (e.g. v4l or alsa). Would having a virtio driver potentially feeding different sub-systems based on configuration be a problem? What do people think? -- Alex Bennée

3 years, 3 months

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Stratos-dev June 2022