linux-kernel - Re: [PATCHv10 03/18] cpu/hotplug: Add support for declaring CPU offlining not supported

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Message-ID: <rju6u37prtr5nf4upcntcy4jcnul6atqmbh6impzqdn3dlo2pj@lqodxa7elohz>
Date: Fri, 19 Apr 2024 16:31:39 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Peter Zijlstra <peterz@...radead.org>, Adrian Hunter <adrian.hunter@...el.com>, 
	Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>, Elena Reshetova <elena.reshetova@...el.com>, 
	Jun Nakajima <jun.nakajima@...el.com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Tom Lendacky <thomas.lendacky@....com>, "Kalra, Ashish" <ashish.kalra@....com>, 
	Sean Christopherson <seanjc@...gle.com>, "Huang, Kai" <kai.huang@...el.com>, Baoquan He <bhe@...hat.com>, 
	kexec@...ts.infradead.org, linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv10 03/18] cpu/hotplug: Add support for declaring CPU
 offlining not supported

On Thu, Apr 18, 2024 at 04:37:09PM +0200, Borislav Petkov wrote:
> On Tue, Apr 09, 2024 at 02:29:55PM +0300, Kirill A. Shutemov wrote:
> > +/* Declare CPU offlining not supported */
> > +void cpu_hotplug_disable_offlining(void)
> > +{
> > +	cpu_maps_update_begin();
> 
> "/*
>  * The following two APIs (cpu_maps_update_begin/done) must be used when
>  * attempting to serialize the updates to cpu_online_mask & cpu_present_mask.
>  */
> void cpu_maps_update_begin(void)
> ..."
> 
> > +	cpu_hotplug_offline_disabled = true;
> 
> but this doesn't do that here.
> 
> Are we doing a one-off here for that variable or what?

Yes, it is one-off. I guess we could use READ_ONCE()/WRITE_ONCE() to
access the variable with the same result. I am not sure why it would be
better.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov