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

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Date:   Wed, 23 Nov 2022 01:14:12 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "peterz@...radead.org" <peterz@...radead.org>,
        "Hansen, Dave" <dave.hansen@...el.com>
CC:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "imammedo@...hat.com" <imammedo@...hat.com>,
        "Gao, Chao" <chao.gao@...el.com>,
        "Brown, Len" <len.brown@...el.com>,
        "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "Huang, Ying" <ying.huang@...el.com>,
        "Williams, Dan J" <dan.j.williams@...el.com>
Subject: Re: [PATCH v7 06/20] x86/virt/tdx: Shut down TDX module in case of
 error

On Tue, 2022-11-22 at 20:33 +0100, Peter Zijlstra wrote:
> 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?

Dave kindly helped to raise this issue and I'll follow up with TDX module guys
to see whether we can remove/ease such limitation.

Thanks!