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

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Message-ID: <6d336ac9-72ad-aae5-0b4c-f30a695d198b@intel.com>
Date:   Mon, 24 May 2021 16:42:08 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>
Cc:     Tony Luck <tony.luck@...el.com>, Andi Kleen <ak@...ux.intel.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Raj Ashok <ashok.raj@...el.com>,
        Sean Christopherson <seanjc@...gle.com>,
        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 4:32 PM, Kuppuswamy Sathyanarayanan wrote:
> Functionally only DMA devices can notice a side effect from
> WBINVD's cache flushing.

This seems to be trying to make some kind of case that the only visible
effects from WBINVD are for DMA devices.  That's flat out wrong.  It
might be arguable that none of the other cases exist in a TDX guest, but
it doesn't excuse making such a broad statement without qualification.

Just grep in the kernel for a bunch of reasons this is wrong.

Where did this come from?