Re: [PATCH] xen/vcpu: ensure no write when runstate handler is NULL

[Roger Pau Monné <roger@xxxxxxxxxxxxxx>]

On Fri, Oct 23, 2026 at 03:33:16PM +0200, Roger Pau Monne wrote:
> Both the normal and the compat versions of
> VCPUOP_register_runstate_memory_area allow registering a NULL handler as a
> way to signal deregistration of the previous area, and
> update_runstate_area() will skip the update when the handler is NULL.
> 
> However when handling the VCPUOP_register_runstate_memory_area hypercall
> itself there's an unconditional attempt to update the newly registered
> runstate area, without taking into account whether it points to NULL.  Skip
> such update if the user-provided handle is NULL.

I've added:

Fixes: 705ea2b54c35 ("New VCPUOP_register_runstate_memory_area hypercall.")

Roger.