linux-kernel - Re: [PATCH 13/13] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

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Message-ID: <20231020123417.2577fm526juwggkf@box.shutemov.name>
Date:   Fri, 20 Oct 2023 15:34:17 +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>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>
Subject: Re: [PATCH 13/13] x86/acpi: Add support for CPU offlining for ACPI
 MADT wakeup method

On Fri, Oct 20, 2023 at 11:21:34AM +0000, Huang, Kai wrote:
> 
> > --- /dev/null
> > +++ b/arch/x86/kernel/acpi/madt.S
> > @@ -0,0 +1,28 @@
> > +#include <linux/linkage.h>
> > +#include <asm/nospec-branch.h>
> > +#include <asm/page_types.h>
> > +#include <asm/processor-flags.h>
> > +
> > +	.text
> > +	.align PAGE_SIZE
> > +SYM_FUNC_START(asm_acpi_mp_play_dead)
> > +	/* Load address of reset vector into RCX to jump when kernel is ready */
> > +	movq	acpi_mp_reset_vector_paddr(%rip), %rcx
> > +
> > +	/* zero out flags, and disable interrupts */
> > +	pushq	$0
> > +	popfq
> > +
> > +	/* Turn off global entries. Following CR3 write will flush them. */
> > +	movq	%cr4, %rdx
> > +	andq	$~(X86_CR4_PGE), %rdx
> > +	movq	%rdx, %cr4
> > +
> > +	/* Switch to identity mapping */
> > +	movq	acpi_mp_pgd(%rip), %rax
> > +	movq	%rax, %cr3
> > +
> > +	/* Jump to reset vector */
> > +	ANNOTATE_RETPOLINE_SAFE
> > +	jmp	*%rcx
> > +SYM_FUNC_END(asm_acpi_mp_play_dead)
> > diff --git a/arch/x86/kernel/acpi/madt_wakeup.c b/arch/x86/kernel/acpi/madt_wakeup.c
> > index 4e92d1d4a5fa..2cc8590ec7a5 100644
> > --- a/arch/x86/kernel/acpi/madt_wakeup.c
> > +++ b/arch/x86/kernel/acpi/madt_wakeup.c
> > @@ -1,12 +1,162 @@
> >  #include <linux/acpi.h>
> >  #include <linux/cpu.h>
> > +#include <linux/delay.h>
> > +#include <linux/memblock.h>
> > +#include <linux/pgtable.h>
> > +#include <linux/sched/hotplug.h>
> >  #include <asm/apic.h>
> > +#include <asm/init.h>
> >  
> >  /* Physical address of the Multiprocessor Wakeup Structure mailbox */
> >  static u64 acpi_mp_wake_mailbox_paddr;
> >  /* Virtual address of the Multiprocessor Wakeup Structure mailbox */
> >  static struct acpi_madt_multiproc_wakeup_mailbox *acpi_mp_wake_mailbox;
> >  
> > +unsigned long acpi_mp_pgd;
> > +u64 acpi_mp_reset_vector_paddr;
> 
> Nit: 
> 
> They are both physical address.  It's a little bit odd for one to use 'unsigned
> long' and the other to use 'u64'.

Okay, I will make them both u64.

> > +
> > +void asm_acpi_mp_play_dead(void);
> > +
> > +static void __init *alloc_pgt_page(void *context)
> > +{
> > +	return memblock_alloc(PAGE_SIZE, PAGE_SIZE);
> > +}
> 
> If I am reading correclty, @context is never used.  It's not used inside this
> function, and all the callers call this with @context = NULL.

Yes. We need the argument to conform to x86_mapping_info::alloc_pgt_page
interface.

> > +
> > +static void acpi_mp_play_dead(void)
> > +{
> > +	idle_task_exit();
> > +	cpuhp_ap_report_dead();
> > +	asm_acpi_mp_play_dead();
> > +}
> > +
> 
> Looks you can use play_dead_common() here, if you take IRQ disable part out from
> the assembly, because play_dead_common() does:
> 
> void play_dead_common(void)
> {               
>         idle_task_exit();
>                 
>         cpuhp_ap_report_dead();                                                
>         
>         local_irq_disable();                                                   
> }

Okay, fair enough.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov