[Qemu-devel] Re: [PATCH 2/9] qemu-kvm: Clean up register access API

[Avi Kivity <avi@redhat.com>]

On 02/19/2010 08:22 PM, Jan Kiszka wrote:
> qemu-kvm's functions for accessing the VCPU registers are
> kvm_arch_load/save_regs. Use them directly instead of going through
> various wrappers. Specifically, we do not need on_vcpu wrapping as all
> users either already run in the related thread or call while the vm is
> stopped. This is now also validated during runtime via asserts.
>
>
> +    assert(kvm_cpu_is_stopped(env) || env->thread_id == kvm_get_thread_id());
>    

The kvm_cpu_is_stopped() part is wrong, for two reasons.  First, a 
future ABI revolution might switch to syscalls and thus make the 
association between vcpu and thread implicit.  This will allow us to 
drop vcpu->mutex, eventually.  Second, kvm_cpu_is_stopped() will be racy 
in a threaded future version of qemu.  All vcpu ioctls should be made 
from the vcpu thread.

Documentation/kvm/api.txt has this to say about the matter:

>  - vcpu ioctls: These query and set attributes that control the operation
>    of a single virtual cpu.
>
>    Only run vcpu ioctls from the same thread that was used to create the
>    vcpu.

So it isn't just me.

-- 
error compiling committee.c: too many arguments to function