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Re: [Qemu-devel] Cubietruck: cannot create KVM guests: "kvm_init_vcpu fa

From: Peter Maydell
Subject: Re: [Qemu-devel] Cubietruck: cannot create KVM guests: "kvm_init_vcpu failed: Invalid argument"
Date: Tue, 9 Dec 2014 13:48:28 +0000

On 9 December 2014 at 12:33, Dr. David Alan Gilbert <address@hidden> wrote:
> * Peter Maydell (address@hidden) wrote:
>> On 9 December 2014 at 11:25, Richard W.M. Jones <address@hidden> wrote:
>> > I really think that qemu should just "do the right thing" though.
>> Tricky, because you have to use the same CPU as the host if
>> you want to use KVM
> That's an unusally strict requirement; is there no concept
> of a common subset that will work on multiple CPUs?
> Is that still true for v8? I can see it making it tricky for users
> with piles of newer/older hosts.

It's a limitation of the kernel implementation -- we don't
attempt to trap things like ID registers, so what the guest
sees is just the host CPU. The architecture provides the means
to trap these and the KVM API allows userspace to ask the
kernel to provide an emulation specifically of a particular
CPU. But the kernel will currently always refuse to emulate
anything other than the host CPU type it's running on.

-- PMM

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