linux-kernel - Re: [RFC v2-fix-v3 1/1] x86/tdx: Skip WBINVD instruction for TDX guest

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Date:   Tue, 8 Jun 2021 16:38:22 -0700
From:   Dave Hansen <dave.hansen@...el.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>,
        Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.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>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [RFC v2-fix-v3 1/1] x86/tdx: Skip WBINVD instruction for TDX
 guest

On 6/8/21 4:32 PM, Dan Williams wrote:
>> Persistent memory is also currently not supported. Another code
>> path that uses WBINVD is the MTRR driver, but EPT/virtualization
>> always disables MTRRs so those are not needed. This all implies
>> WBINVD is not needed with current TDX.
> Let's drop the last three paragraphs and just say something like:
> "This is one of a series of patches to usages of wbinvd for protected
> guests. For now this just addresses the one known path that TDX
> executes, ACPI reboot. Its usage can be elided because FOO reason and
> all the other ACPI_FLUSH_CPU_CACHE usages can be elided because BAR
> reason"

A better effort at transparency can be made here:

	This patches the one WBINVD instance which has been encountered
	in practice: ACPI reboot.  Assume no other instance will be
	encountered.