Second, KVM is a fork of the Qemu executable.
#PROXMOX SERIAL PORT PASS THROUGH BILLING CODE#
Since it is a new processor mode of execution, the code doesn't have to be modified in any way.Īpart from the processor state switching, the kernel module also handles a few low-level parts of the emulation like the MMU registers (used to handle VM) and some parts of the PCI emulated hardware. The guest state has its own set of ring states, but privileged ring0 instructions fall back to the hypervisor code. KVM is a couple of things: first it is a Linux kernel module-now included in mainline-that switches the processor into a new 'guest' state. This is a lot faster than plain Qemu because most code is unchanged, but still has to transform ring0 code (most of the code in the VM's kernel), so performance still suffers. All the peripheral hardware emulation is done in Qemu. The difference is that instead of recompiling the code, it calls KQemu to scan/patch/execute it. In that case, userspace Qemu still allocates all the RAM for the emulated machine, and loads the code. To make it as efficient as possible on x86 Linux, there's a kernel module called KQemu that handles this.īeing a kernel module, KQemu is able to execute most code unchanged, replacing only the lowest-level ring0-only instructions.
In the specific case where both source and target are the same architecture (like the common case of x86 on x86), it still has to parse the code to remove any 'privileged instructions' and replace them with context switches. To emulate more than just the processor, Qemu includes a long list of peripheral emulators: disk, network, VGA, PCI, USB, serial/parallel ports, etc. Mainly it works by a special 'recompiler' that transforms binary code written for a given processor into another one (say, to run MIPS code on a PPC mac, or ARM in an x86 PC). You use it to emulate machines, it is very flexible and portable.
#PROXMOX SERIAL PORT PASS THROUGH BILLING SOFTWARE#
QEmu is a complete and standalone software of its own.
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