Re: [RESEND PATCH v4 12/15] fs/resctrl: Hide kmode_cpus[_list] on groups not bound to kernel-mode

[Babu Moger <babu.moger@amd.com>]

Hi Reinette,


On 8/10/26 22:30, Reinette Chatre wrote:
> Hi Babu,
> 
> On 7/7/26 2:50 PM, Babu Moger wrote:
>> kmode_cpus and kmode_cpus_list describe the CPU scope for the rdtgroup that
>> owns the active kernel-mode binding. They are meaningful only for
>> resctrl_kcfg.k_rdtgrp.
>>
>> On groups that do not own the kernel-mode binding, they appear as inactive
>> stubs and can let user space inspect or update state that does not apply to
>> that group.
>>
>> Hide kmode_cpus and kmode_cpus_list on groups that are not bound to
>> kernel-mode. Keep the files hidden when groups are created, show them when
>> rdtgroup_config_kmode() binds the group, and hide them again when the
>> binding is released.
>>
>> Signed-off-by: Babu Moger <babu.moger@amd.com>
>> ---
>> v4: Updated the changelog and code comments.
>>
>> v3: New patch to hide/show "kmode_cpus" and "kmode_cpus_list" when kernel
>>      modes binding changes.
>> ---
>>   fs/resctrl/rdtgroup.c | 33 +++++++++++++++++++++++++++++++++
>>   1 file changed, 33 insertions(+)
>>
>> diff --git a/fs/resctrl/rdtgroup.c b/fs/resctrl/rdtgroup.c
>> index 413d3ff14546..c537846d9264 100644
>> --- a/fs/resctrl/rdtgroup.c
>> +++ b/fs/resctrl/rdtgroup.c
>> @@ -1127,6 +1127,35 @@ static int resctrl_kernel_mode_show(struct kernfs_open_file *of,
>>   	return ret;
>>   }
>>   
>> +/**
>> + * resctrl_kmode_files_set_visible() - Toggle visibility of the per-group
>> + *		kernel-mode CPU files under @rdtgrp.
>> + * @rdtgrp:	Resctrl group whose "kmode_cpus" / "kmode_cpus_list" files
>> + *		should be hidden or shown.
>> + * @visible:	%true to expose the files, %false to hide them via
>> + *		kernfs_show().
>> + *
>> + * Each file is resolved independently as a sibling under @rdtgrp->kn.
>> + * Failures from kernfs_find_and_get() are deliberately ignored, allowing
>> + * callers to invoke this before activation, during group creation, or when
>> + * the kernel-mode binding is updated.
>> + */
>> +static void resctrl_kmode_files_set_visible(struct rdtgroup *rdtgrp, bool visible)
>> +{
>> +	/* Keep in sync with res_common_files[] entries for these files. */
>> +	static const char * const files[] = { "kmode_cpus", "kmode_cpus_list" };
>> +	struct kernfs_node *kn;
>> +	int i;
>> +
>> +	for (i = 0; i < ARRAY_SIZE(files); i++) {
>> +		kn = kernfs_find_and_get(rdtgrp->kn, files[i]);
>> +		if (!kn)
>> +			continue;
>> +		kernfs_show(kn, visible);
>> +		kernfs_put(kn);
>> +	}
>> +}
>> +
>>   /**
>>    * rdtgroup_config_kmode_reset() - Tear down the kernel-mode binding on @rdtgrp
>>    * @rdtgrp:	Resctrl group whose kernel-mode binding is being released.
>> @@ -1155,6 +1184,7 @@ static void rdtgroup_config_kmode_reset(struct rdtgroup *rdtgrp,
>>   
>>   out_clear:
>>   	cpumask_clear(&rdtgrp->kmode_cpu_mask);
>> +	resctrl_kmode_files_set_visible(rdtgrp, false);
>>   	rdtgrp->kmode = false;
>>   }
>>   
>> @@ -3068,6 +3098,7 @@ static int rdt_get_tree(struct fs_context *fc)
>>   	if (ret)
>>   		goto out_closid_exit;
>>   
>> +	resctrl_kmode_files_set_visible(&rdtgroup_default, false);
>>   	kernfs_activate(rdtgroup_default.kn);
>>   
>>   	ret = rdtgroup_create_info_dir(rdtgroup_default.kn);
>> @@ -4098,6 +4129,7 @@ static int rdtgroup_mkdir_mon(struct kernfs_node *parent_kn,
>>   		goto out_unlock;
>>   	}
>>   
>> +	resctrl_kmode_files_set_visible(rdtgrp, false);
>>   	kernfs_activate(rdtgrp->kn);
>>   
>>   	/*
>> @@ -4142,6 +4174,7 @@ static int rdtgroup_mkdir_ctrl_mon(struct kernfs_node *parent_kn,
>>   	if (ret)
>>   		goto out_closid_free;
>>   
>> +	resctrl_kmode_files_set_visible(rdtgrp, false);
>>   	kernfs_activate(rdtgrp->kn);
>>   
>>   	ret = rdtgroup_init_alloc(rdtgrp);
> 
> Sprinkling these resctrl_kmode_files_set_visible() in every path that creates these files
> seem error prone. Could this be simplified with a new, for example, rftype::create_hidden that
> will instruct the file to be created hidden. This would just create the file correctly from the
> beginning and eliminate these calls that go back and "fix things up" for kernel mode use. This may
> also eliminate the need to ignore errors in resctrl_kmode_files_set_visible() making this
> more robust while making it obvious how the file visibility is actually connected to the
> kernel mode since that would be the only points where the file visibility is changed.
>
Already discussed to create the hidden files for all the groups during 
the group creation. Then call resctrl_kmode_files_set_visible() based on 
visibility requirement when group is added/removed from global kernel mode.

https://lore.kernel.org/lkml/98568620-7e61-4d43-b72c-5866a7d3bca1@intel.com/.

Thanks
Babu