linux-kernel - Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN

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Message-ID: <b867f002-bb62-94b0-1e13-f2b8520011e6@intel.com>
Date:   Wed, 17 Nov 2021 11:11:31 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Borislav Petkov <bp@...en8.de>,
        Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        "VMware, Inc." <pv-drivers@...are.com>
Subject: Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV

On 11/17/21 10:48 AM, Borislav Petkov wrote:
> On Wed, Nov 17, 2021 at 10:46:30AM -0800, Sathyanarayanan Kuppuswamy wrote:
>> TDX has a requirement to use HLT paravirt calls (which is currently
>> listed under PARAVIRT_XXL). Once we submit a patch to move it
>> under CONFIG_PARAVIRT, we will drop this dependency.
> You already have this patch in some set:
> 
> https://lore.kernel.org/r/20211009053747.1694419-2-sathyanarayanan.kuppuswamy@linux.intel.com
> 
> So what's this churn for?

The churn is my doing.  It occurred to me that we could toss the
aforementioned patch out of the set by using:

	depends on PARAVIRT_XXL

instead of:

	depends on PARAVIRT

Especially since PARAVIRT_XXL seems pretty common in distro kernels.
But, I didn't realize quite how reviled PARAVIRT_XXL was.

So, first of all, _this_ patch is a proper cleanup.  We should merge it
or something like it either way.

As for TDX, my preference (obviously) is to keep the "depends on
PARAVIRT_XXL", reviled as it may be.  It's the literal truth at this
point: TDX guest support depends on PARAVIRT_XXL functionality.  There
is no shortage of ways to remove that dependency (expand PARAVIRT or
custom idle), which makes me very confident that we are not painting
ourselves into a corner here.