On Wed, Nov 19, 2025 at 11:50:59AM +0530, Shrikanth Hegde wrote:
> This is helper patch which could be used to set the range of CPUs as
> paravirt. One could make use of this for quick testing of this infra
> instead of writing arch specific code.
>
> This is currently not meant be merged, since paravirt sysfs file is meant
> to be Read-Only.
>
> echo 100-200,600-700 > /sys/devices/system/cpu/paravirt
> cat /sys/devices/system/cpu/paravirt
> 100-200,600-700
>
> echo > /sys/devices/system/cpu/paravirt
> cat /sys/devices/system/cpu/paravirt
>
> Signed-off-by: Shrikanth Hegde <[email protected]>
> ---
> drivers/base/cpu.c | 48 ++++++++++++++++++++++++++++++++++++++++++++--
> 1 file changed, 46 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
> index 59ceae217b22..043e4f4ce1a9 100644
> --- a/drivers/base/cpu.c
> +++ b/drivers/base/cpu.c
> @@ -375,12 +375,57 @@ static int cpu_uevent(const struct device *dev, struct
> kobj_uevent_env *env)
> #endif
>
> #ifdef CONFIG_PARAVIRT
> +static ssize_t store_paravirt_cpus(struct device *dev,
> + struct device_attribute *attr,
> + const char *buf, size_t count)
> +{
> + cpumask_var_t temp_mask;
> + int retval = 0;
> +
> + if (!alloc_cpumask_var(&temp_mask, GFP_KERNEL))
> + return -ENOMEM;
> +
> + retval = cpulist_parse(buf, temp_mask);
> + if (retval)
> + goto free_mask;
> +
> + /* ALL cpus can't be marked as paravirt */
> + if (cpumask_equal(temp_mask, cpu_online_mask)) {
> + retval = -EINVAL;
> + goto free_mask;
> + }
> + if (cpumask_weight(temp_mask) > num_online_cpus()) {
> + retval = -EINVAL;
> + goto free_mask;
> + }
> +
> + /* No more paravirt cpus */
> + if (cpumask_empty(temp_mask)) {
> + cpumask_copy((struct cpumask *)&__cpu_paravirt_mask, temp_mask);
> + } else {
> + cpumask_copy((struct cpumask *)&__cpu_paravirt_mask, temp_mask);
> +
> + /* Enable tick on nohz_full cpu */
> + int cpu;
> + for_each_cpu(cpu, temp_mask) {
> + if (tick_nohz_full_cpu(cpu))
> + tick_nohz_dep_set_cpu(cpu, TICK_DEP_BIT_SCHED);
> + }
> + }
> +
> + retval = count;
> +
> +free_mask:
> + free_cpumask_var(temp_mask);
> + return retval;
> +}
> +
> static ssize_t print_paravirt_cpus(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> return sysfs_emit(buf, "%*pbl\n", cpumask_pr_args(cpu_paravirt_mask));
> }
> -static DEVICE_ATTR(paravirt, 0444, print_paravirt_cpus, NULL);
> +static DEVICE_ATTR(paravirt, 0644, print_paravirt_cpus, store_paravirt_cpus);
DEVICE_ATTR_RW()?
And where is the documentation update for this sysfs file change?
> #endif
>
> const struct bus_type cpu_subsys = {
> @@ -675,7 +720,6 @@ static void __init cpu_register_vulnerabilities(void)
> put_device(dev);
> }
> }
> -
> #else
Why is this change needed?
thanks,
greg k-h
