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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Xen Rust VirtIO demos work breakdown for Project Stratos
Hi, The following is a breakdown (as best I can figure) of the work needed to demonstrate VirtIO backends in Rust on the Xen hypervisor. It requires work across a number of projects but notably core rust and virtio enabling in the Xen project (building on the work EPAM has already done) and the start of enabling rust-vmm crate to work with Xen. The first demo is a fairly simple toy to exercise the direct hypercall approach for a unikernel backend. On it's own it isn't super impressive but hopefully serves as a proof of concept for the idea of having backends running in a single exception level where latency will be important. The second is a much more ambitious bridge between Xen and vhost-user to allow for re-use of the existing vhost-user backends with the bridge acting as a proxy for what would usually be a full VMM in the type-2 hypervisor case. With that in mind the rust-vmm work is only aimed at doing the device emulation and doesn't address the larger question of how type-1 hypervisors can be integrated into the rust-vmm hypervisor model. A quick note about the estimates. They are exceedingly rough guesses plucked out of the air and I would be grateful for feedback from the appropriate domain experts on if I'm being overly optimistic or pessimistic. The links to the Stratos JIRA should be at least read accessible to all although they contain the same information as the attached document (albeit with nicer PNG renderings of my ASCII art ;-). There is a Stratos sync-up call next Thursday: https://calendar.google.com/event?action=TEMPLATE&tmeid=MWpidm5lbzM5NjlydnAxdWxvc2s4aGI0ZGpfMjAyMTA5MzBUMTUwMDAwWiBjX2o3bmdpMW84cmxvZmtwZWQ0cjVjaDk4bXZnQGc&tmsrc=c_j7ngi1o8rlofkped4r5ch98mvg%40group.calendar.google.com and I'm sure there will also be discussion in the various projects (hence the wide CC list). The Stratos calls are open to anyone who wants to attend and we welcome feedback from all who are interested. So on with the work breakdown: ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ STRATOS PLANNING FOR 21 TO 22 Alex Bennée ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ Table of Contents ───────────────── 1. Xen Rust Bindings ([STR-51]) .. 1. Upstream an "official" rust crate for Xen ([STR-52]) .. 2. Basic Hypervisor Interactions hypercalls ([STR-53]) .. 3. [#10] Access to XenStore service ([STR-54]) .. 4. VirtIO support hypercalls ([STR-55]) 2. Xen Hypervisor Support for Stratos ([STR-56]) .. 1. Stable ABI for foreignmemory mapping to non-dom0 ([STR-57]) .. 2. Tweaks to tooling to launch VirtIO guests 3. rust-vmm support for Xen VirtIO ([STR-59]) .. 1. Make vm-memory Xen aware ([STR-60]) .. 2. Xen IO notification and IRQ injections ([STR-61]) 4. Stratos Demos .. 1. Rust based stubdomain monitor ([STR-62]) .. 2. Xen aware vhost-user master ([STR-63]) 1 Xen Rust Bindings ([STR-51]) ══════════════════════════════ There exists a [placeholder repository] with the start of a set of x86_64 bindings for Xen and a very basic hello world uni-kernel example. This forms the basis of the initial Xen Rust work and will be available as a [xen-sys crate] via cargo. [STR-51] <https://linaro.atlassian.net/browse/STR-51> [placeholder repository] <https://gitlab.com/cardoe/oxerun.git> [xen-sys crate] <https://crates.io/crates/xen-sys> 1.1 Upstream an "official" rust crate for Xen ([STR-52]) ──────────────────────────────────────────────────────── To start with we will want an upstream location for future work to be based upon. The intention is the crate is independent of the version of Xen it runs on (above the baseline version chosen). This will entail: • ☐ agreeing with upstream the name/location for the source • ☐ documenting the rules for the "stable" hypercall ABI • ☐ establish an internal interface to elide between ioctl mediated and direct hypercalls • ☐ ensure the crate is multi-arch and has feature parity for arm64 As such we expect the implementation to be standalone, i.e. not wrapping the existing Xen libraries for mediation. There should be a close (1-to-1) mapping between the interfaces in the crate and the eventual hypercall made to the hypervisor. Estimate: 4w (elapsed likely longer due to discussion) [STR-52] <https://linaro.atlassian.net/browse/STR-52> 1.2 Basic Hypervisor Interactions hypercalls ([STR-53]) ─────────────────────────────────────────────────────── These are the bare minimum hypercalls implemented as both ioctl and direct calls. These allow for a very basic binary to: • ☐ console_io - output IO via the Xen console • ☐ domctl stub - basic stub for domain control (different API?) • ☐ sysctl stub - basic stub for system control (different API?) The idea would be this provides enough hypercall interface to query the list of domains and output their status via the xen console. There is an open question about if the domctl and sysctl hypercalls are way to go. Estimate: 6w [STR-53] <https://linaro.atlassian.net/browse/STR-53> 1.3 [#10] Access to XenStore service ([STR-54]) ─────────────────────────────────────────────── This is a shared configuration storage space accessed via either Unix sockets (on dom0) or via the Xenbus. This is used to access configuration information for the domain. Is this needed for a backend though? Can everything just be passed direct on the command line? Estimate: 4w [STR-54] <https://linaro.atlassian.net/browse/STR-54> 1.4 VirtIO support hypercalls ([STR-55]) ──────────────────────────────────────── These are the hypercalls that need to be implemented to support a VirtIO backend. This includes the ability to map another guests memory into the current domains address space, register to receive IOREQ events when the guest knocks at the doorbell and inject kicks into the guest. The hypercalls we need to support would be: • ☐ dmop - device model ops (*_ioreq_server, setirq, nr_vpus) • ☐ foreignmemory - map and unmap guest memory The DMOP space is larger than what we need for an IOREQ backend so I've based it just on what arch/arm/dm.c exports which is the subset introduced for EPAM's virtio work. Estimate: 12w [STR-55] <https://linaro.atlassian.net/browse/STR-55> 2 Xen Hypervisor Support for Stratos ([STR-56]) ═══════════════════════════════════════════════ These tasks include tasks needed to support the various different deployments of Stratos components in Xen. [STR-56] <https://linaro.atlassian.net/browse/STR-56> 2.1 Stable ABI for foreignmemory mapping to non-dom0 ([STR-57]) ─────────────────────────────────────────────────────────────── Currently the foreign memory mapping support only works for dom0 due to reference counting issues. If we are to support backends running in their own domains this will need to get fixed. Estimate: 8w [STR-57] <https://linaro.atlassian.net/browse/STR-57> 2.2 Tweaks to tooling to launch VirtIO guests ───────────────────────────────────────────── There might not be too much to do here. The EPAM work already did something similar for their PoC for virtio-block. Essentially we need to ensure: • ☐ DT bindings are passed to the guest for virtio-mmio device discovery • ☐ Our rust backend can be instantiated before the domU is launched This currently assumes the tools and the backend are running in dom0. Estimate: 4w 3 rust-vmm support for Xen VirtIO ([STR-59]) ════════════════════════════════════════════ This encompasses the tasks required to get a vhost-user server up and running while interfacing to the Xen hypervisor. This will require the xen-sys.rs crate for the actual interface to the hypervisor. We need to work out how a Xen configuration option would be passed to the various bits of rust-vmm when something is being built. [STR-59] <https://linaro.atlassian.net/browse/STR-59> 3.1 Make vm-memory Xen aware ([STR-60]) ─────────────────────────────────────── The vm-memory crate is the root crate for abstracting access to the guests memory. It currently has multiple configuration builds to handle difference between mmap on Windows and Unix. Although mmap isn't directly exposed the public interfaces support a mmap like interface. We would need to: • ☐ work out how to expose foreign memory via the vm-memory mechanism I'm not sure if this just means implementing the GuestMemory trait for a GuestMemoryXen or if we need to present a mmap like interface. Estimate: 8w [STR-60] <https://linaro.atlassian.net/browse/STR-60> 3.2 Xen IO notification and IRQ injections ([STR-61]) ───────────────────────────────────────────────────── The KVM world provides for ioeventfd (notifications) and irqfd (injection) to signal asynchronously between the guest and the backend. As far a I can tell this is currently handled inside the various VMMs which assume a KVM backend. While the vhost-user slave code doesn't see the register_ioevent/register_irqfd events it does deal with EventFDs throughout the code. Perhaps the best approach here would be to create a IOREQ crate that can create EventFD descriptors which can then be passed to the slaves to use for notification and injection. Otherwise there might be an argument for a new crate that can encapsulate this behaviour for both KVM/ioeventd and Xen/IOREQ setups? Estimate: 8w? [STR-61] <https://linaro.atlassian.net/browse/STR-61> 4 Stratos Demos ═══════════════ These tasks cover the creation of demos that brig together all the previous bits of work to demonstrate a new area of capability that has been opened up by Stratos work. 4.1 Rust based stubdomain monitor ([STR-62]) ──────────────────────────────────────────── This is a basic demo that is a proof of concept for a unikernel style backend written in pure Rust. This work would be a useful precursor for things such as the RTOS Dom0 on a safety island ([STR-11]) or as a carrier for the virtio-scmi backend. The monitor program will periodically poll the state of the other domains and echo their status to the Xen console. Estimate: 4w #+name: stub-domain-example #+begin_src ditaa :cmdline -o :file stub_domain_example.png Dom0 | DomU | DomStub | | : /-------------\ : | |cPNK | | | | | | | | | | /------------------------------------\ | | GuestOS | | |cPNK | | | | | EL0 | Dom0 Userspace (xl tools, QEMU) | | | | | /---------------\ | | | | | | |cYEL | \------------------------------------/ | | | | | | +------------------------------------+ | | | | | Rust Monitor | EL1 |cA1B Dom0 Kernel | | | | | | | +------------------------------------+ | \-------------/ | \---------------/ -------------------------------------------------------------------------------=------------------ +-------------------------------------------------------------------------------------+ EL2 |cC02 Xen Hypervisor | +-------------------------------------------------------------------------------------+ #+end_src [STR-62] <https://linaro.atlassian.net/browse/STR-62> [STR-11] <https://linaro.atlassian.net/browse/STR-11> 4.2 Xen aware vhost-user master ([STR-63]) ────────────────────────────────────────── Usually the master side of a vhost-user system is embedded directly in the VMM itself. However in a Xen deployment their is no overarching VMM but a series of utility programs that query the hypervisor directly. The Xen tooling is also responsible for setting up any support processes that are responsible for emulating HW for the guest. The task aims to bridge the gap between Xen's normal HW emulation path (ioreq) and VirtIO's userspace device emulation (vhost-user). The process would be started with some information on where the virtio-mmio address space is and what the slave binary will be. It will then: • map the guest into Dom0 userspace and attach to a MemFD • register the appropriate memory regions as IOREQ regions with Xen • create EventFD channels for the virtio kick notifications (one each way) • spawn the vhost-user slave process and mediate the notifications and kicks between the slave and Xen itself #+name: xen-vhost-user-master #+begin_src ditaa :cmdline -o :file xen_vhost_user_master.png Dom0 DomU | | | | | | +-------------------+ +-------------------+ | | |----------->| | | | vhost-user | vhost-user | vhost-user | : /------------------------------------\ | slave | protocol | master | | | | | (existing) |<-----------| (rust) | | | | +-------------------+ +-------------------+ | | | ^ ^ | ^ | | Guest Userspace | | | | | | | | | | | IOREQ | | | | | | | | | | | v v V | | \------------------------------------/ +---------------------------------------------------+ | +------------------------------------+ | ^ ^ | ioctl ^ | | | | | | iofd/irqfd eventFD | | | | | | Guest Kernel | | +---------------------------+ | | | | | +-------------+ | | | | | | | | virtio-dev | | | Host Kernel V | | | | +-------------+ | +---------------------------------------------------+ | +------------------------------------+ | ^ | | ^ | hyper | | | ----------------------=------------- | -=--- | ----=------ | -----=- | --------=------------------ | call | Trap | | IRQ V | V | +-------------------------------------------------------------------------------------+ | | ^ | ^ | | | +-------------+ | | EL2 | Xen Hypervisor | | | | +-------------------------------+ | | | +-------------------------------------------------------------------------------------+ #+end_src [STR-63] <https://linaro.atlassian.net/browse/STR-63> -- Alex Bennée
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