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 17:36:21 -0700
From:   Andi Kleen <ak@...ux.intel.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        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


  that.

> I thought we discussed that there are other considerations for wbinvd
> besides DMA? In any event this paragraph is actively misleading
> because it disregards ACPI and Persistent Memory secure-erase whose
> usages of wbinvd have nothing to do with DMA.


In this case they would be broken in KVM too.


> I would much prefer a
> patch to shutdown all the known wbinvd users as a precursor to this
> patch rather than assuming it's ok to simply ignore it. You have
> mentioned that TDX does not need to use those paths, but rather than
> assume they can't be used why not do the audit to explicitly disable
> them? Otherwise this statement seems to imply that the audit has not
> been done.

We're not assuming it. We know it because KVM does it since forever.

All we want to do is do the same as KVM.

-Andi