linux-kernel - Re: [PATCH v2] x86: Skip WBINVD instruction for VM guest

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Date:   Mon, 6 Dec 2021 08:53:50 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Kuppuswamy Sathyanarayanan 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        "H . Peter Anvin" <hpa@...or.com>, Tony Luck <tony.luck@...el.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v2] x86: Skip WBINVD instruction for VM guest

On 12/6/21 8:39 AM, Dan Williams wrote:
>> But, the trick is that we need a contract.  A contract requires a
>> "meeting of the minds" first.
> The WBINVD requirement in sleep states is about getting cache contents
> out to to power preserved domain before the CPU turns off. The bare
> metal host handles that requirement. The conversation that needs to be
> had is with the ACPI specification committee to clarify that virtual
> machines have no responsibility to flush caches. We can do that as a
> Code First proposal to the ACPI Specification Working Group.

Sounds sane to me.  So, we effectively go to the ACPI folks and say that
Linux isn't going to do WBINVD in virtualized environments any more.
That was effectively the approach that the first patch in this thread did:

> https://lore.kernel.org/all/20211116005027.2929297-1-sathyanarayanan.kuppuswamy@linux.intel.com/

Right?