Re: [Xen-devel] [PATCH V2 2/2] xen: Introduce VM_EVENT_FLAG_SET_REGISTERS

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.09.15 at 15:31, <rcojocaru@xxxxxxxxxxxxxxx> wrote:
> A previous version of this patch dealing with support for skipping
> the current instruction when a vm_event response requested it
> computed the instruction length in the hypervisor, adding non-trivial
> code dependencies. This patch allows a userspace vm_event client to
> simply request that the guest's EIP is set to an arbitary value,
> computed by the introspection application. In the future, other
> registers can also be set via a vm_event reply by using this flag.
> The VCPU needs to be paused for this flag to take effect.
> 
> Signed-off-by: Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>
> 
> ---
> Changes since V1:
>  - Renamed the patch (VM_EVENT_FLAG_SET_EIP ->
>    VM_EVENT_FLAG_SET_REGISTERS).
>  - As suggested by Tamas Lengyel, EIP is now being set via a dedicated
>    generic vm_event_set_registers() function that can be extended to
>    set other registers in the future.

Isn't it a bad move to call the thing "set registers" but have it set
just EIP? If going forward you were to add more registers, you'd
need new flags anyway I suppose, and hence the public interface
part of this should be reverted (while the other internal
abstraction seems fine to me).

Jan


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