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

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Date:   Mon, 6 Dec 2021 09:51:07 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dave Hansen <dave.hansen@...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 Mon, Dec 6, 2021 at 8:54 AM Dave Hansen <dave.hansen@...el.com> wrote:
>
> 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?

Correct, my reviewed-by was based on that observation, and now we can
close the loop by proposing the specification change.