linux-kernel - Re: [PATCHv3 14/14] x86/acpi: Add support for CPU offlining for ACPI MADT wakeup method

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Date:   Mon, 4 Dec 2023 22:43:45 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>
CC:     "kexec@...ts.infradead.org" <kexec@...ts.infradead.org>,
        "linux-coco@...ts.linux.dev" <linux-coco@...ts.linux.dev>,
        "ashish.kalra@....com" <ashish.kalra@....com>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "thomas.lendacky@....com" <thomas.lendacky@....com>,
        "Hunter, Adrian" <adrian.hunter@...el.com>,
        "Reshetova, Elena" <elena.reshetova@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "seanjc@...gle.com" <seanjc@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "bhe@...hat.com" <bhe@...hat.com>,
        "Nakajima, Jun" <jun.nakajima@...el.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "bp@...en8.de" <bp@...en8.de>,
        "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCHv3 14/14] x86/acpi: Add support for CPU offlining for ACPI
 MADT wakeup method

> 
> > > +
> > >  int __init acpi_parse_mp_wake(union acpi_subtable_headers *header,
> > >  			      const unsigned long end)
> > >  {
> > >  	struct acpi_madt_multiproc_wakeup *mp_wake;
> > >  
> > >  	mp_wake = (struct acpi_madt_multiproc_wakeup *)header;
> > > -	if (BAD_MADT_ENTRY(mp_wake, end))
> > > +	if (!mp_wake)
> > > +		return -EINVAL;
> > 
> > I think you can keep the BAD_MADT_ENTRY() check as a standard check, and ...
> 
> No. BAD_MADT_ENTRY() will fail if the struct version is V0 because the
> size will be smaller than sizeof(struct acpi_madt_multiproc_wakeup).

Ah OK.  Maybe worth a comment like below?


	/*
	 * Cannot use the standard BAD_MADT_ENTRY() to sanity check the
@mp_wake
	 * entry.  'sizeof (struct acpi_madt_multiproc_wakeup)' can be larger
	 * than the actual size of the MP wakeup entry in ACPI table because
the
	 * 'reset_vector' is only available in the V2 MP wakeup structure.
	 */


[...]

> --- a/arch/x86/kernel/reboot.c
> +++ b/arch/x86/kernel/reboot.c
> @@ -878,10 +878,14 @@ static int crash_nmi_callback(unsigned int val, struct pt_regs *regs)
>  	cpu_emergency_disable_virtualization();
>  
>  	atomic_dec(&waiting_for_crash_ipi);
> -	/* Assume hlt works */
> -	halt();
> -	for (;;)
> -		cpu_relax();
> +
> +	if (smp_ops.crash_play_dead) {
> +	    smp_ops.crash_play_dead();
> +	} else {
> +		halt();
> +		for (;;)
> +			cpu_relax();
> +	}
>  

Agree this is better than explicitly checking TDX guest. :-)