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

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Date:   Tue, 22 Nov 2022 20:33:16 +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, 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 22, 2022 at 11:24:48AM -0800, Dave Hansen wrote:

> > Not intialize TDX on busy NOHZ_FULL cpus and hard-limit the cpumask of
> > all TDX using tasks.
> 
> I don't think that works.  As I mentioned to Thomas elsewhere, you don't
> just need to initialize TDX on the CPUs where it is used.  Before the
> module will start working you need to initialize it on *all* the CPUs it
> knows about.  The module itself has a little counter where it tracks
> this and will refuse to start being useful until it gets called
> thoroughly enough.

That's bloody terrible, that is. How are we going to make that work with
the SMT mitigation crud that forces the SMT sibilng offline?

Then the counters don't match and TDX won't work.

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?