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Hannes Mehnert 2016-07-02 17:50:12 +01:00
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@ -13,7 +13,7 @@ As described [earlier](https://hannes.nqsb.io/Posts/OperatingSystem), MirageOS i
Xen is a hypervisor, providing concrete device drivers for the actual hardware of a physical machine, memory management, scheduling, etc. The initial release of Xen was done in 2003, since then the code size and code complexity of Xen is growing. It also has various different mechanisms for virtualisation, hardware assisted ones or purely software based ones, some where the guest operating system needs to cooperate others where it does not need to cooperate. Xen is a hypervisor, providing concrete device drivers for the actual hardware of a physical machine, memory management, scheduling, etc. The initial release of Xen was done in 2003, since then the code size and code complexity of Xen is growing. It also has various different mechanisms for virtualisation, hardware assisted ones or purely software based ones, some where the guest operating system needs to cooperate others where it does not need to cooperate.
Since 2005, Intel CPUs (as well as AMD CPUs) provide hardware assistance for virtualisation (the VT-x extension), since 2008 extended page tables (EPT) are around which allow a guest to safely access the MMU. Those features gave rise to much smaller hypervisors, such as KVM (mainly Linux), bhyve (FreeBSD), xhyve (MacOSX), vmm (OpenBSD), which do not need to emulate the MMU and other things in software. The boot sequence in those hypervisors uses kexec or multiboot, instead of doing all the 16 bit, 32 bit, 64 bit mode changes manually. Since 2005, Intel CPUs (as well as AMD CPUs) provide hardware assistance for virtualisation (the VT-x extension), since 2008 extended page tables (EPT) are around which allow a guest to safely access the MMU. Those features gave rise to much smaller hypervisors, such as KVM (mainly Linux), [bhyve](http://bhyve.org) (FreeBSD), [xhyve](http://xhyve.org) (MacOSX), [vmm](http://undeadly.org/cgi?action=article&sid=20150831183826) (OpenBSD), which do not need to emulate the MMU and other things in software. The boot sequence in those hypervisors uses kexec or multiboot, instead of doing all the 16 bit, 32 bit, 64 bit mode changes manually.
MirageOS initially targeted only Xen, in 2015 there was a port to use rumpkernel (a modularised NetBSD), and 2016 [solo5](https://github.com/djwillia/solo5) emerged where you can run MirageOS on. Solo5 comes in two shapes, either as `ukvm` on top of KVM, or as a multiboot image using `virtio` interfaces (block and network, plus a serial console). Solo5 is only ~1000 lines of code (plus dlmalloc), and ISC-licensed. MirageOS initially targeted only Xen, in 2015 there was a port to use rumpkernel (a modularised NetBSD), and 2016 [solo5](https://github.com/djwillia/solo5) emerged where you can run MirageOS on. Solo5 comes in two shapes, either as `ukvm` on top of KVM, or as a multiboot image using `virtio` interfaces (block and network, plus a serial console). Solo5 is only ~1000 lines of code (plus dlmalloc), and ISC-licensed.