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

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Message-ID: <nh7cihzlsjtoddtec6m62biqdn62k3ka5svs6m64qekhpebu5z@dkplwad2urgp>
Date: Tue, 11 Jun 2024 18:47:05 +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 05:01:55PM +0300, Kirill A. Shutemov wrote:
> 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.

Borislav, given this code deduplication effort is not trivial, maybe we
can do it as a separate patchset on top of this one?

I also wounder if it makes sense to combine ident_map.c and set_memory.c.
There's some overlap between the two.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov