linux-kernel - Re: [PATCHv4 14/14] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

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Date: Fri, 22 Dec 2023 14:19:45 +0300
From: "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
To: "Huang, Kai" <kai.huang@...el.com>
Cc: "tglx@...utronix.de" <tglx@...utronix.de>,
	"mingo@...hat.com" <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>, "bp@...en8.de" <bp@...en8.de>,
	"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
	"Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
	"Reshetova, Elena" <elena.reshetova@...el.com>,
	"Nakajima, Jun" <jun.nakajima@...el.com>,
	"rafael@...nel.org" <rafael@...nel.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"sathyanarayanan.kuppuswamy@...ux.intel.com" <sathyanarayanan.kuppuswamy@...ux.intel.com>,
	"Hunter, Adrian" <adrian.hunter@...el.com>,
	"thomas.lendacky@....com" <thomas.lendacky@....com>,
	"ashish.kalra@....com" <ashish.kalra@....com>,
	"kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
	"seanjc@...gle.com" <seanjc@...gle.com>,
	"bhe@...hat.com" <bhe@...hat.com>,
	"linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCHv4 14/14] x86/acpi: Add support for CPU offlining for ACPI
 MADT wakeup method

On Tue, Dec 05, 2023 at 11:36:55PM +0000, Huang, Kai wrote:
> 
> > +
> > +static void acpi_mp_stop_other_cpus(int wait)
> > +{
> > +	smp_shutdown_nonboot_cpus(smp_processor_id());
> > +}
> 
> Is this and ...
> 
> +	smp_ops.stop_other_cpus = acpi_mp_stop_other_cpus;
> 
> ... this below still needed?
> 
> I think the current native_stop_other_cpus() should just work given you have set
> up ...
> 
> +	smp_ops.crash_play_dead = crash_acpi_mp_play_dead;
> 
> ... for TDX guest?

To make it work stop_this_cpu() would need to be modified to use
smp_ops.crash_play_dead() instead of native_halt(). But name of the
callback doesn't match the function, so I renamed it to
smp_ops.stop_this_cpu().

> Sorry for saying this late.  I think we can also use kernel_ident_mapping_init()
> to do the init_transition_pgtable()?  We can set struct x86_mapping_info::offset
> to __PAGE_OFFSET to do that?
> 
> Looks set_up_temporary_mappings() in arch/x86/power/hibernate_64.c uses the same
> trick.
> 
> Anyway I am not sure how many LoC (assuming can do) can be saved so up to you.

Yeah. Benefit is not clear to me. I will leave it as is.


> 
> It's a little bit sad such cleanup code isn't in common code, e.g., with a 
> 
> 	void (*free_pgt_page)(void *);
> 
> to allow the user to specify how to free the page table.
> 
> But this can be future job if needed.

I will consider moving this cleanup in common code. And maybe fix other
users of kernel_ident_mapping_init(). Nobody seems to care to cleanup page
tables on ENOMEM.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov