Re: [PATCH for-4.22? 6/9] domctl: handle XEN_DOMCTL_getvcpuinfo without acquiring domctl lock

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Jun 15, 2026 at 04:15:12PM +0200, Jan Beulich wrote:
> Like for XEN_DOMCTL_getdomaininfo there's no need to hold the domctl
> lock for XEN_DOMCTL_getvcpuinfo. While moving the code also switch to
> using domain_vcpu().
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> Tentatively-acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>

Acked-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Some suggestions below.

> 
> --- a/xen/common/domctl.c
> +++ b/xen/common/domctl.c
> @@ -546,6 +546,33 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xe
>      if ( ret )
>          goto domctl_out_unlock_rcuonly;
>  
> +    switch ( op->cmd )
> +    {
> +    case XEN_DOMCTL_getvcpuinfo:
> +    {
> +        const struct vcpu *v;
> +
> +        if ( (v = domain_vcpu(d, op->u.getvcpuinfo.vcpu)) == NULL )

Since you are moving the code anyway, I would rather do:

        const struct vcpu *v = domain_vcpu(d, op->u.getvcpuinfo.vcpu);

        if ( !v )
            ...

> +        {
> +            ret = -ENOENT;
> +            goto domctl_out_unlock_rcuonly;
> +        }
> +
> +        op->u.getvcpuinfo.online   = !(v->pause_flags & VPF_down);
> +        op->u.getvcpuinfo.blocked  = !!(v->pause_flags & VPF_blocked);
> +        op->u.getvcpuinfo.running  = v->is_running;
> +        op->u.getvcpuinfo.cpu_time = vcpu_runstate_get_running(v);
> +        op->u.getvcpuinfo.cpu      = v->processor;
> +
> +        copyback = true;
> +        goto domctl_out_unlock_rcuonly;
> +    }
> +
> +    default:
> +        /* Everything else handled further up or further down. */
> +        break;
> +    }

As you are introducing this here, we might want to also move
XEN_DOMCTL_shadow_op handling into this new switch block: with the RCU
taken and after the xsm_domctl() call.

Thanks, Roger.