linux-kernel - Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu initialization

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Date:   Tue, 14 Feb 2023 15:12:50 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, tglx@...utronix.de,
        seanjc@...gle.com, pbonzini@...hat.com, dan.j.williams@...el.com,
        rafael.j.wysocki@...el.com, kirill.shutemov@...ux.intel.com,
        ying.huang@...el.com, reinette.chatre@...el.com,
        len.brown@...el.com, tony.luck@...el.com, ak@...ux.intel.com,
        isaku.yamahata@...el.com, chao.gao@...el.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com, david@...hat.com,
        bagasdotme@...il.com, sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v9 07/18] x86/virt/tdx: Do TDX module per-cpu
 initialization

On Mon, Feb 13, 2023 at 10:07:30AM -0800, Dave Hansen wrote:
> On 2/13/23 03:59, Kai Huang wrote:
> > @@ -247,8 +395,17 @@ int tdx_enable(void)
> >  		ret = __tdx_enable();
> >  		break;
> >  	case TDX_MODULE_INITIALIZED:
> > -		/* Already initialized, great, tell the caller. */
> > -		ret = 0;
> > +		/*
> > +		 * The previous call of __tdx_enable() may only have
> > +		 * initialized part of present cpus during module
> > +		 * initialization, and new cpus may have become online
> > +		 * since then.
> > +		 *
> > +		 * To make sure all online cpus are TDX-runnable, always
> > +		 * do per-cpu initialization for all online cpus here
> > +		 * even the module has been initialized.
> > +		 */
> > +		ret = __tdx_enable_online_cpus();
> 
> I'm missing something here.  CPUs get initialized through either:
> 
>  1. __tdx_enable(), for the CPUs around at the time
>  2. tdx_cpu_online(), for hotplugged CPUs after __tdx_enable()
> 
> But, this is a third class.  CPUs that came online after #1, but which
> got missed by #2.  How can that happen?

offline CPUs, start TDX crap, online CPUs.