linux-kernel - Re: [RFC PATCH v3 04/10] sched/core: Dont allow to use CPU marked as paravirt

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Message-ID: <d5605402-b37a-411a-aabc-842b5a924dbe@amd.com>
Date: Thu, 11 Sep 2025 10:46:12 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>, <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>, <linux-kernel@...r.kernel.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <gregkh@...uxfoundation.org>
CC: <vschneid@...hat.com>, <iii@...ux.ibm.com>, <huschle@...ux.ibm.com>,
	<rostedt@...dmis.org>, <dietmar.eggemann@....com>, <vineeth@...byteword.org>,
	<jgross@...e.com>, <pbonzini@...hat.com>, <seanjc@...gle.com>
Subject: Re: [RFC PATCH v3 04/10] sched/core: Dont allow to use CPU marked as
 paravirt

Hello Shrikanth,

On 9/10/2025 11:12 PM, Shrikanth Hegde wrote:
> @@ -2462,8 +2462,13 @@ static inline bool is_cpu_allowed(struct task_struct *p, int cpu)
>  		return cpu_online(cpu);
>  
>  	/* Non kernel threads are not allowed during either online or offline. */
> -	if (!(p->flags & PF_KTHREAD))
> -		return cpu_active(cpu);
> +	if (!(p->flags & PF_KTHREAD)) {
> +		/* A user thread shouldn't be allowed on a paravirt cpu */
> +		if (is_cpu_paravirt(cpu))
> +			return false;
> +		else

nit. redundant "else". I think this can be simplified as:

    return !is_cpu_paravirt(cpu) && cpu_active(cpu);

> +			return cpu_active(cpu);
> +	}

-- 
Thanks and Regards,
Prateek