linux-kernel - Re: [PATCHv10 04/18] cpu/hotplug, x86/acpi: Disable CPU offlining for ACPI MADT wakeup

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Date: Tue, 23 Apr 2024 18:02:58 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
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 04/18] cpu/hotplug, x86/acpi: Disable CPU offlining
 for ACPI MADT wakeup

On Tue, Apr 09, 2024 at 02:29:56PM +0300, Kirill A. Shutemov wrote:
> ACPI MADT doesn't allow to offline CPU after it got woke up.

In all your text: s/woke/woken/g

> 
> Currently CPU hotplug is prevented based on the confidential computing
> attribute which is set for Intel TDX. But TDX is not the only possible
> user of the wake up method.
> 
> Disable CPU offlining on ACPI MADT wakeup enumeration.

Something's missing in that "justification". It should explain why
CC_ATTR_HOTPLUG_DISABLED is not needed anymore.

And looking at patch 3, I'm still unclear as to why this change is done.
Is it that the "ACPI MADT mailbox wakeup method" is going to be used by
TDX guests now too so that you don't need CC_ATTR_HOTPLUG_DISABLED
anymore?

It seems that if acpi_parse_mp_wake() finds an ok wakeup entry, then
offlining is disabled...

Or is it something else?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette