linux-kernel - Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of error

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Date:   Wed, 30 Nov 2022 12:09:31 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Kai Huang <kai.huang@...el.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, linux-mm@...ck.org, 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, bagasdotme@...il.com,
        sagis@...gle.com, imammedo@...hat.com
Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of
 error

On Tue, Nov 29 2022 at 13:40, Dave Hansen wrote:
> On 11/22/22 11:33, Peter Zijlstra wrote:
>> Can we get this limitiation removed and simply let the module throw a
>> wobbly (error) when someone tries and use TDX without that logical CPU
>> having been properly initialized?
>
> It sounds like we can at least punt the limitation away from the OS's
> purview.
>
> There's actually a multi-step process to get a "real" TDX module loaded.
>  There's a fancy ACM (Authenticated Code Module) that's invoked via
> GETSEC[ENTERACCS] and an intermediate module loader.  That dance used to
> be done in the kernel, but we talked the BIOS guys into doing it instead.
>
> I believe these per-logical-CPU checks _can_ also be punted out of the
> TDX module itself and delegated to one of these earlier module loading
> phases that the BIOS drives.
>
> I'm still a _bit_ skeptical that the checks are needed in the first
> place.  But, as long as they're hidden from the OS, I don't see a need
> to be too cranky about it.

Right.

> In the end, we could just plain stop doing the TDH.SYS.LP.INIT code in
> the kernel.

Which in turn makes all the problems we discussed go away.

> Unless someone screams, I'll ask the BIOS and TDX module folks to look
> into this.

Yes, please.

Thanks,

        tglx