Re: [Qemu-devel] [PATCH 01/22] configure: factor out list of supported Xen/KVM/HAX targets

["Daniel P. Berrange" <berrange@redhat.com>]

On Tue, Jul 04, 2017 at 11:44:41AM +0200, Paolo Bonzini wrote:
> 
> 
> On 04/07/2017 10:28, Daniel P. Berrange wrote:
> >> +supported_kvm_target() {
> >> +    test "$kvm" = "yes" || return 1
> >> +    glob "$1" "*-softmmu" || return 1
> >> +    case "${1%-softmmu}:$cpu" in
> >> +        arm:arm | aarch64:aarch64 | \
> >> +        i386:i386 | i386:x86_64 | i386:x32 | \
> >> +        x86_64:i386 | x86_64:x86_64 | x86_64:x32 | \
> > 
> > IIUC, 'x86_64:i386' is claiming that you can run x86_64
> > KVM guests on an i386 host. I thought that was impossible,
> > only 32-on-64 being allowed not 64-on-32.
> 
> You can use qemu-system-x86_64 to run i386 KVM guests, by disabling long
> mode with -cpu.  It's not a common scenario though.

Wow, obscure :-)

> 
> >> +        mips:mips | mipsel:mips | \
> >> +        ppc:ppc | ppcemb:ppc | ppc64:ppc | \
> >> +        ppc:ppc64 | ppcemb:ppc64 | ppc64:ppc64 | \
> > 
> > Same question here with ppc64:ppc suggesting you can
> > run 64-bit guest with KVM on a 32-bit host ?
> 
> I'm not sure about this one, but right now it is allowed so this patch
> is not changing anything.
> 
> >> +        s390x:s390x)
> >> +            return 0
> >> +        ;;
> >> +    esac
> >> +    return 1
> >> +}
> >> +
> >> +supported_xen_target() {
> >> +    test "$xen" = "yes" || return 1
> >> +    glob "$1" "*-softmmu" || return 1
> >> +    case "${1%-softmmu}:$cpu" in
> >> +        arm:arm | aarch64:aarch64 | \
> >> +        i386:i386 | i386:x86_64 | x86_64:i386 | x86_64:x86_64)
> > This again is claiming support for 64-bit guests with Xen on a
> > 32-bit host, which AFAIK is impossible.
> 
> 32-bit dom0 with 64-bit guests actually is not only possible, but also
> widely used.

Oh, i guess I'm missing the distinction between 64-bit hypervisor vs
32-bit dom-0, which still lets you use 64-bit dom-U.

In that case,

Reviewed-by: Daniel P. Berrange <berrange@redhat.com>


Regards,
Daniel
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