linux-kernel - Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

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Message-ID: <20240610134020.GCZmcCRFxuObyv1W_d@fat_crate.local>
Date: Mon, 10 Jun 2024 15:40:20 +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>,
	Ard Biesheuvel <ardb@...nel.org>, Baoquan He <bhe@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>, kexec@...ts.infradead.org,
	linux-hyperv@...r.kernel.org, linux-acpi@...r.kernel.org,
	linux-coco@...ts.linux.dev, linux-kernel@...r.kernel.org,
	Tao Liu <ltao@...hat.com>
Subject: Re: [PATCHv11 18/19] x86/acpi: Add support for CPU offlining for
 ACPI MADT wakeup method

On Fri, Jun 07, 2024 at 06:14:28PM +0300, Kirill A. Shutemov wrote:
>   I was able to address this issue by switching cpa_lock to a mutex.
>   However, this solution will only work if the callers for set_memory
>   interfaces are not called from an atomic context. I need to verify if
>   this is the case.

Dunno, I'd be nervous about this. Althouth from looking at

   ad5ca55f6bdb ("x86, cpa: srlz cpa(), global flush tlb after splitting big page and before doing cpa")

I don't see how "So that we don't allow any other cpu" can't be done
with a mutex. Perhaps the set_memory* interfaces should be usable in as
many contexts as possible.

Have you run this with lockdep enabled?

> - The function __flush_tlb_all() in kernel_(un)map_pages_in_pgd() must be
>   called with preemption disabled. Once again, I am unsure why this has
>   not caused issues in the EFI case.

It could be because EFI does all that setup on the BSP only before the
others have arrived but I don't remember anymore... It is more than
a decade ago when I did this...

Thx.

-- 
Regards/Gruss,
    Boris.

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