linux-kernel - Re: [HELPER PATCH 1] sysfs: Provide write method for paravirt

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <7b468240-f614-4a7e-983a-c264acdc1159@linux.ibm.com>
Date: Wed, 19 Nov 2025 15:31:23 +0530
From: Shrikanth Hegde <sshegde@...ux.ibm.com>
To: Christophe Leroy <christophe.leroy@...roup.eu>,
        Greg KH <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, tglx@...utronix.de, yury.norov@...il.com,
        maddy@...ux.ibm.com, srikar@...ux.ibm.com, pbonzini@...hat.com,
        seanjc@...gle.com, kprateek.nayak@....com, vschneid@...hat.com,
        iii@...ux.ibm.com, huschle@...ux.ibm.com, rostedt@...dmis.org,
        dietmar.eggemann@....com
Subject: Re: [HELPER PATCH 1] sysfs: Provide write method for paravirt



On 11/19/25 1:50 PM, Christophe Leroy wrote:
> 
> 
> Le 19/11/2025 à 09:08, Shrikanth Hegde a écrit :
>> Hi Greg.
>>
>> On 11/19/25 1:12 PM, Greg KH wrote:
>>> 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 <sshegde@...ux.ibm.com>
>>>> ---
>>>>   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()?
>>
>> ok.
>>
>>>
>>> And where is the documentation update for this sysfs file change?
>>>
>>
>> [RFC PATCH v4 11/17] has the documentation of this sysfs file.
> 
> There is a problem in the way you sent this patch and the other helper 
> patch. They appear in the cover letter of your series are part of it but 
> at the end the series is only sent with 15 patches over 17, and the last 
> two patches appear as independent from the series:
> 
> Series at https://patchwork.ozlabs.org/project/linuxppc-dev/list/? 
> series=482680
> 
> Other patches are on their own: https://patchwork.ozlabs.org/project/ 
> linuxppc-dev/list/?submitter=87866
> 

I edited the patch header before sending. Wanted to say they are debug patches.
Thought "helper" maybe a name. My bad.

I didn't realize that it could seen an separate patches :(
So sorry. I thought it would come up as thread of the series. Like it showed up in
https://lore.kernel.org/all/20251119062100.1112520-12-sshegde@linux.ibm.com/#r

Should I resend the series?