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

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Message-ID: <hidvykk3yan5rtlhum6go7j3lwgrcfcgxlwyjug3osfakw2x6f@4ohvo23zaesv>
Date: Mon, 10 Jun 2024 17:01:55 +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>, 
	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 Mon, Jun 10, 2024 at 03:40:20PM +0200, Borislav Petkov wrote:
> 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?

Yes, it booted to the shell just fine. However, that doesn't prove
anything. The set_memory_* function has many obscured cases.

> > - 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...

Are you okay with this? Disabling preemption looks strange, but I don't
see a better option.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov