linux-kernel - Re: [PATCHv5.1 14/16] x86/smp: Add smp_ops.stop_this

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Date: Tue, 9 Jan 2024 03:04:15 +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>,
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	<x86@...nel.org>
Subject: Re: [PATCHv5.1 14/16] x86/smp: Add smp_ops.stop_this_cpu() callback


> > > @@ -835,6 +835,13 @@ void __noreturn stop_this_cpu(void *dummy)
> > >  	 */
> > >  	cpumask_clear_cpu(cpu, &cpus_stop_mask);
> > >  
> > > +#ifdef CONFIG_SMP
> > > +	if (smp_ops.stop_this_cpu) {
> > > +		smp_ops.stop_this_cpu();
> > > +		unreachable();
> > > +	}
> > > +#endif
> > 
> > If I read correctly this will result in stop_this_cpu() having different
> > behaviour for SMP and !SMP build for TDX guest.  For example, AFAICT
> > machine_halt() also calls stop_this_cpu() on local cpu after it stops other
> > cpus.  So for the local cpu, in SMP build it will calls into BIOS's reset vector
> > but in !SMP it will call native_halt().
> 
> It doesn't make a difference in practice: both halt and giving CPU to
> BIOS will be unrecoverable operation. Both are equally acceptable for
> machine_halt().
> 

OK fair enough. :-)