XEN(4)

🌸 NAME 🌸

okay bestie, this is the xen(4) page, and the NAME line is xen — Xen Hypervisor Support. That's the whole name, and yes, it's giving “hypervisor but make it a group project.” 💖

✨ SYNOPSIS ✨

FreeBSD supports running both as a Xen guest and as a Xen host on amd64 hardware. Guest support is limited to HVM and PVH modes, while host support is limited to PVH mode only.

Xen support is built by default in the i386 and amd64 GENERIC kernels; note however that host mode is only available on amd64.

bestie, quick vibe check: host mode is amd64-only. No cap, fr fr. 🫶

💅 DESCRIPTION 💅

ngl, the Xen Hypervisor lets multiple virtual machines run on a single computer system — main character energy, periodt. ✨

When first released, Xen required that i386 kernels be compiled "para-virtualized" as the x86 instruction set was not fully virtualizable. Primarily, para-virtualization modifies the virtual memory system to use hypervisor calls (hypercalls) rather than direct hardware instructions to modify the TLB, although para-virtualized device drivers were also required to access resources such as virtual network interfaces and disk devices.

With later instruction set extensions from AMD and Intel to support fully virtualizable instructions, unmodified virtual memory systems can also be supported; this is referred to as hardware-assisted virtualization (HVM and PVH). HVM configurations may either rely on transparently emulated hardware peripherals, or para-virtualized drivers, which are aware of virtualization, and hence able to optimize certain behaviors to improve performance or semantics. PVH configurations rely on para-virtualized drivers exclusively for IO — fr fr.

FreeBSD Para-virtualized device drivers are required in order to support certain functionality, such as processing management requests, returning idle physical memory pages to the hypervisor, etc. 💜

🎀 Xen device drivers 🎀

These para-virtualized drivers are supported:

• balloon — allow physical memory pages to be returned to the hypervisor as a result of manual tuning or automatic policy. It's giving “give the RAM back, bestie.” 🎈
• blkback — exports local block devices or files to other Xen domains where they can then be imported via blkfront. Sharing is caring, but make it block storage. 💽
• blkfront — import block devices from other Xen domains as local block devices, to be used for file systems, swap, etc. Your fave imported goods, lowkey. 🛍️
• console — export the low-level system console via the Xen console service. The backstage pass of the kernel world. 🎟️
• control — process management operations from Domain 0, including power off, reboot, suspend, crash, and halt requests. The responsible older sibling of the group chat. 👑
• evtchn — expose Xen events via the /dev/xen/evtchn special device. Event notifications but make it a special file. 🔔
• gntdev — allow access to the grant table interface via the /dev/xen/gntdev special device. The grant table is the VIP list, iykyk. 🪪
• netback — export local network interfaces to other Xen domains where they can be imported via netfront. Networking, but shared. 🌐
• netfront — import network interfaces from other Xen domains as local network interfaces, which may be used for IPv4, IPv6, etc. Yes bestie, IPv6 too. 🛜
• privcmd — allow issuing hypercalls via the /dev/xen/privcmd special device. Hypercall access, very “I know a guy.” 🕶️
• timer — implementation of a one-shot high resolution per-CPU timer using the hypercall interface. Tick tock, but per-CPU and high resolution. ⏱️
• acpi cpu — when running as a host forwards power management related information from ACPI to the hypervisor for better performance management. Power info handoff, slay. 🔋
• xenpci — represents the Xen PCI device, an emulated PCI device that is exposed to HVM domains. This device allows detection of the Xen hypervisor, and provides interrupt and shared memory services required to interact with the hypervisor. The little PCI device that could. 🧚
• xenstore — information storage space shared between domains. Shared notes app for Xen domains. 📝

🦋 HISTORY 🦋

Support for xen first appeared in FreeBSD 8.1 — iconic. Support for host mode was added in 11.0 . 🕰️

👑 AUTHORS 👑

FreeBSD support for Xen was first added by Kip Macy <kmacy@FreeBSD.org> and Doug Rabson <dfr@FreeBSD.org>. Further refinements were made by Justin Gibbs <gibbs@FreeBSD.org>, Adrian Chadd <adrian@FreeBSD.org>, Colin Percival <cperciva@FreeBSD.org>, and Roger Pau Monné <royger@FreeBSD.org>. This manual page was written by Robert Watson <rwatson@FreeBSD.org>, and Roger Pau Monné <royger@FreeBSD.org>. Absolute icons, every one. 💅 iykyk.

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The footer energy is Debian and January 8, 2024 — mwah, bestie 💋✨