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Date:   Wed, 9 Feb 2022 20:11:57 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Sean Christopherson <seanjc@google.com>
Cc:     Kai Huang <kai.huang@intel.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        tglx@linutronix.de, mingo@redhat.com, dave.hansen@intel.com,
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Subject: Re: [PATCHv2 00/29] TDX Guest: TDX core support
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On Wed, Feb 09, 2022 at 04:50:08PM +0000, Sean Christopherson wrote:
> On Wed, Feb 09, 2022, Borislav Petkov wrote:
> > On Thu, Feb 10, 2022 at 12:48:31AM +1300, Kai Huang wrote:
> > > Are you suggesting even for now we can start to put TDX host support to
> > > arch/x86/coco/tdx/ ?
> > 
> > That's exactly what I'm suggesting. The TDX stuff is not upstream so
> > nothing's cast in stone yet. This way there won't be any unpleasant code
> > movements later.
> 
> I strongly prefer we put the guest and host code in separate directories.  Both
> TDX and SEV are big enough that they'll benefit from splitting up files, having
> to fight over file names or tag all files with guest/host will get annoying.
> 
> I do like the idea of arch/x86/coco though.  The most straightforward approach
> would be:
> 
>   arch/x86/coco/guest/
>   arch/x86/coco/host/
> 
> but that doesn't provide any extensibility on the host virtualization side, e.g.
> to land non-coco, non-KVM-specific host virtualization code (we have a potential
> use case for this).  If that happens, we'd end up with x86 KVM having code and
> dependencies split across:
> 
>   arch/x86/coco/host
>   arch/x86/kvm/
>   arch/x86/???/
> 
> An alternative idea would be to mirror what generic KVM does (virt/kvm/), and do:
> 
>   arch/x86/coco/<guest stuff>
>   arch/x86/virt/<"generic" x86 host virtualization stuff>
>   arch/x86/virt/coco/<host coco stuff>
>   arch/x86/virt/kvm/
> 
> Though I can already hear the stable trees and downstream kernels crying out in
> horror at moving arch/x86/kvm :-)

Hmmm, so I am still thinking about guest-only when we're talking about
arch/x86/coco/.

Lemme look at the other virt things:

the kvm host virt stuff is in:

arch/x86/kvm/

 (btw, this is where the SEV host stuff is: arch/x86/kvm/svm/sev.c)

arch/x86/hyperv/ - looks like hyperv guest stuff

arch/x86/xen/ - xen guest stuff

arch/x86/kernel/cpu/vmware.c - vmware guest stuff

arch/x86/kernel/cpu/acrn.c - Acorn guest stuff

So we have a real mess. :-(

Not surprised though. So that last thing you're suggesting kinda makes
sense but lemme tweak it a bit:

arch/x86/coco/<guest stuff>
arch/x86/virt/<"generic" x86 host virtualization stuff>
arch/x86/virt/tdx/ - no need for the "coco" thing - TDX is nothing but coco. TDX host
stuff

arch/x86/virt/sev/ - ditto

and we'll keep arch/x86/kvm because of previous precedents with other
things I've enumerated above.

Hmmm?

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette