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

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Message-ID: <2d9172c5-e1e7-bf94-c52b-0e9bc5b5b319@intel.com>
Date:   Mon, 13 Feb 2023 10:07:30 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     linux-mm@...ck.org, peterz@...radead.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 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?