linux-kernel - Re: [PATCH v9 04/18] x86/virt/tdx: Add skeleton to initialize TDX on demand

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Date:   Tue, 14 Feb 2023 21:08:09 +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>,
        "david@...hat.com" <david@...hat.com>,
        "bagasdotme@...il.com" <bagasdotme@...il.com>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "kirill.shutemov@...ux.intel.com" <kirill.shutemov@...ux.intel.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "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 v9 04/18] x86/virt/tdx: Add skeleton to initialize TDX on
 demand

On Tue, 2023-02-14 at 09:23 -0800, Dave Hansen wrote:
> On 2/14/23 04:46, Peter Zijlstra wrote:
> > On Tue, Feb 14, 2023 at 12:59:11AM +1300, Kai Huang wrote:
> > > Use a state machine protected by mutex to make sure the initialization
> > > will only be done once, as tdx_enable() can be called multiple times
> > > (i.e. KVM module can be reloaded) and be called concurrently by other
> > > kernel components in the future.
> > I still object to doing tdx_enable() at kvm module load.
> > 
> > kvm.ko gets loaded unconditionally on boot, even if I then never use
> > kvm.
> > 
> > This stuff needs to be done when an actual VM is created, not before.
> 
> The actually implementation of this is hidden over in the KVM side of
> this.  But, tdx_enable() and all of this jazz should not be called on
> kvm.ko load.  It'll happen when the KVM tries to start the first TDX VM.
> 
> I think what Kai was thinking of was *this* sequence:
> 
>  1. insmod kvm.ko
>  2. Start a TDX guest, tdx_enable() gets run
>  3. rmmod kvm
>  4. insmod kvm.ko (again)
>  5. Start another TDX guest, run tdx_enable() (again)
> 
> The rmmod/insmod pair is what triggers the second call of tdx_enable().

Yes.  The point is tdx_enable() can get called multi times.

We can discuss more when to enable TDX at KVM side, and I don't want to speak
for KVM maintainers, but this is actually not that relevant to this series.

In the changelog, I just said: 

"...initialize TDX until there is a real need (e.g when requested by KVM)".  

I didn't say exactly when KVM will call this.