Re: [PATCH v7 5/7] xen/cpupool: Don't allow removing cpu0 from cpupool0

[Luca Fancellu <Luca.Fancellu@xxxxxxx>]

> On 11 Apr 2022, at 16:20, Luca Fancellu <Luca.Fancellu@xxxxxxx> wrote:
> 
> Cpu0 must remain in cpupool0, otherwise some operations like moving cpus
> between cpupools, cpu hotplug, destroying cpupools, shutdown of the host,
> might not work in a sane way.
> 
> Signed-off-by: Luca Fancellu <luca.fancellu@xxxxxxx>
> ---
> Changes in v7:
> - new patch
> ---
> xen/common/sched/cpupool.c | 8 +++++++-
> 1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/common/sched/cpupool.c b/xen/common/sched/cpupool.c
> index 86a175f99cd5..0a93bcc631bf 100644
> --- a/xen/common/sched/cpupool.c
> +++ b/xen/common/sched/cpupool.c
> @@ -572,6 +572,7 @@ static long cf_check cpupool_unassign_cpu_helper(void 
> *info)
>  * possible failures:
>  * - last cpu and still active domains in cpupool
>  * - cpu just being unplugged
> + * - Attempt to remove boot cpu from cpupool0
>  */
> static int cpupool_unassign_cpu(struct cpupool *c, unsigned int cpu)
> {
> @@ -582,7 +583,12 @@ static int cpupool_unassign_cpu(struct cpupool *c, 
> unsigned int cpu)
>     debugtrace_printk("cpupool_unassign_cpu(pool=%u,cpu=%d)\n",
>                       c->cpupool_id, cpu);
> 
> -    if ( !cpu_online(cpu) )
> +    /*
> +     * Cpu0 must remain in cpupool0, otherwise some operations like moving 
> cpus
> +     * between cpupools, cpu hotplug, destroying cpupools, shutdown of the 
> host,
> +     * might not work in a sane way.
> +     */
> +    if ( (!c->cpupool_id && !cpu) || !cpu_online(cpu) )
>         return -EINVAL;
> 
>     master_cpu = sched_get_resource_cpu(cpu);
> -- 
> 2.17.1
> 

Hi,

I’m going to address the comment on this serie before re-pushing it, I see there
are no comments on this patch, so I’m wondering, when you have time, if you
can give me some feedback on this one.

Cheers,
Luca