I know that Linux OS's are typically multi-programmed, which means that multiple processes can be active at the same time. Can there be multiple kernels executing at the same time?
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3 Answers
Sort of. Check out User-mode Linux.
With most virtualization solutions (xen, virtualbox, vmware and the likes), you certainly have multiple kernels running at the same time on a single machine.
- 1But of course only one kernel is running "on the real hardware" as the hypervisor.mattdm– mattdm2011-01-02 12:52:50 +00:00Commented Jan 2, 2011 at 12:52
- Some high end servers support multiple kernels running concurrently on the same machine (a.k.a. physical domains) but I don't think Linux is supported on these boxes. Solaris definitely is.jlliagre– jlliagre2011-01-03 17:21:35 +00:00Commented Jan 3, 2011 at 17:21
- — I believe in those cases what it really means is that there's a firmware-level hypervisor mediating access to the actual hardware.mattdm– mattdm2011-02-22 20:36:44 +00:00Commented Feb 22, 2011 at 20:36
- There is no such need with physical domains. The hardware resources are dispatched between the domains then are electrically isolated. Thanks to this isolation, there is no need for an underlying hypervisor layer on these kind of servers.jlliagre– jlliagre2011-02-22 21:55:59 +00:00Commented Feb 22, 2011 at 21:55
Yes, multiple kernels can run on your hardware at the same time - though maybe not quite the way you're thinking.
x86_64 systems produced in the last few decades include firmware that continues to run after "your" OS starts up, and this firmware is sufficiently complex to qualify as a kernel - or even multiple kernels.
These include UEFI and SMM firmware that executes on the main CPU, as well as firmware that runs on the ME (now CSME), ISH, or IE, which are x86 CPUs embedded in Intel chipsets. The ISH or IE seem limited, but the ME can access all physical memory and most or all hardware in the system.
AMD systems have a platform security processor or PSP, though from the details available so far it seems less omnipotent than the ME.
Ron Minnich discusses these kernels in his talk Replace Your Exploit-Ridden Firmware with Linux; the slide at 1:34 and the one following (2:45) are particularly relevant. These slides are also pages 3-4 of this pdf.
