Re: [Qemu-devel] [RFC 0/2] target-arm: Provide '-cpu host' when running KVM

[Peter Maydell]

On 14 August 2013 10:11, Alexander Graf <address@hidden> wrote:
> You're right, the main difference is that KVM doesn't have any
> idea what a "host" style CPU is. It only knows how to report to QEMU
> what the current host CPU would be, so that anything from VCPU_INIT
> onwards is 100% identical regardless of whether the user said
> -cpu host or -cpu xxx.
>
> I'm still puzzled on how this will work with BIG.little btw.

The rough idea is that for BIG.little the kernel must trap the
ID registers at least (so that the vcpu seems consistent to the
guest whether it's running on the big or the little core). For
"-cpu host" the guest would see whatever is the most low-overhead
for the kernel to provide (ie assuming the big and little CPUs
are roughly-similar you could make -cpu host provide something
that looks to the guest like the big CPU and don't have to trap
quite as much as you would for providing a vcpu that wasn't the
same as either the big or little one).

-- PMM