linux-kernel - Re: [RFC v2-fix-v2 2/2] x86/tdx: Ignore WBINVD instruction for TDX guest

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Date:   Mon, 24 May 2021 21:32:15 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>
Cc:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC v2-fix-v2 2/2] x86/tdx: Ignore WBINVD instruction for TDX
 guest

On 5/24/21 7:13 PM, Andi Kleen wrote:
> I don't see any point of all of this. We really just want to be the same
> as KVM. Not get into the business of patching a bazillion sub systems
> that cannot be used in TDX anyways.

Andi, there's a fundamental difference between KVM the hypervisor and a
TDX guest: KVM the hypervisor runs unknown guests, and lots of them.

TD guest support as a whole has to handle one thing: running *one* Linux
kernel.  Further, the guest support shares a source tree with that
kernel.  TD guest support doesn't have to run random binaries for which
there is no source.  All of the source is *RIGHT* *THERE*.

The only reason TD guest support would have to fall back to KVM's dirty
tricks is a desire to treat the rest of the kernel like a black box.
KVM frankly has no other choice.  TD guest support has all the choices
in the world.