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

[Alexander Graf <agraf@suse.de>]

On 14.08.2013, at 11:07, Peter Maydell wrote:

> On 14 August 2013 09:46, Alexander Graf <agraf@suse.de> wrote:
>> So can we access those even when the vcpu hasn't been init'ed yet? If so, how about the following flow of things for -cpu host:
>> 
>>  - QEMU fetches host target type via ioctl (how will this work for big-little?)
>>  - QEMU fetches ID registers, feature flags, etc via one-reg (or are they also available via auxv?), puts them into its internal "this is my cpu type" fields for the cpu object / class.
>>  - QEMU calls VCPU_INIT with the type it fetched via ioctl.
> 
> Curiously enough this is pretty much exactly what this patch
> actually does (except we don't bother to actually stash the ID
> register values because we know they'll never be used).

Heh, you mean I should read patches after 0/x too? :)

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.


Alex