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

[Alexander Graf]

On 14.08.2013, at 11:23, Peter Maydell wrote:

> 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).

So -cpu host in this case wouldn't actually expose the host CPU 1:1, but 
instead a cortex-a15 even when it's run on an a7 BIG.little core. I see.


Alex