Is a 64bit host expected to support running a 32bit guest OS in qemu/kvm? Or do archs need to match?
Chris Murphy
Dne středa, 16. října 2013 16:12:21 CEST, Chris Murphy napsal(a):
Is a 64bit host expected to support running a 32bit guest OS in qemu/kvm? Or do archs need to match?
I believe, if the CPU does support that (are we talking aboout x86_64?), KVM won't stand in the way
anyways, you can always use qemu without kvm, then you can run anything-on-anything (if performance is not an issue)
K.
On 10/16/2013 08:12 AM, Chris Murphy wrote:
Is a 64bit host expected to support running a 32bit guest OS in qemu/kvm? Or do archs need to match?
64-bit guets on 64-bit host exposing a 64-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 64-bit host exposing only a 32-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 64-bit host exposing a 64-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 32-bit host (necessarily exposing a 32-bit environment) - works just fine; supported, uses hardware acceleration (but gets less testing, as few people run virt hosts in 32-bit mode).
No support for running a 64-bit guest on a 32-bit host (hardware just doesn't expose enough memory).
Cross arch testing - works just fine, but slower (uses qemu emulation rather than hardware accelation), and a bit harder to support, but still useful; can only support a bit width in the guest <= bit width in the host.
Eric Blake wrote:
No support for running a 64-bit guest on a 32-bit host (hardware just doesn't expose enough memory).
Your competitors software supports this configuration as long as virtualization extensions are available on the host CPU.
Not that I'm requesting it, but a little FYI for Chris (as you probably know this).
On Oct 16, 2013, at 9:02 AM, Eric Blake eblake@redhat.com wrote:
On 10/16/2013 08:12 AM, Chris Murphy wrote:
Is a 64bit host expected to support running a 32bit guest OS in qemu/kvm? Or do archs need to match?
64-bit guets on 64-bit host exposing a 64-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 64-bit host exposing only a 32-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 64-bit host exposing a 64-bit environment - works just fine; supported, uses hardware acceleration.
32-bit guest on 32-bit host (necessarily exposing a 32-bit environment)
- works just fine; supported, uses hardware acceleration (but gets less
testing, as few people run virt hosts in 32-bit mode).
No support for running a 64-bit guest on a 32-bit host (hardware just doesn't expose enough memory).
OK thanks. Followups are:
Q1: Where in virt-manager is the setting to expose 32bit/64bit environment? I don't see this in Processor. I do see Architecture: x86_64 in Overview>Hypervisor Details but I have no way to change it.
Q2: Should this test case: https://fedoraproject.org/wiki/QA:Testcase_Install_to_Current_KVM
Cover all of the above combinations, minus 64-bit guest on 32-bit host? Or is 64/64, and either 64/32 or 32/32 sufficient?
Chris Murphy