linux-kernel - Re: [RFC v2 27/32] x86/tdx: Exclude Shared bit from __PHYSICAL

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Date:   Thu, 20 May 2021 19:33:22 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        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>, linux-kernel@...r.kernel.org
Subject: Re: [RFC v2 27/32] x86/tdx: Exclude Shared bit from __PHYSICAL_MASK

On Thu, May 20, 2021, Kuppuswamy, Sathyanarayanan wrote:
> Hi Dave,
> 
> On 5/19/21 9:14 AM, Dave Hansen wrote:
> > On 4/26/21 11:01 AM, Kuppuswamy Sathyanarayanan wrote:
> > > From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> > > 
> > > tdx_shared_mask() returns the mask that has to be set in a page
> > > table entry to make page shared with VMM.
> > 
> > Here's a rewrite:
> > 
> > Just like MKTME, TDX reassigns bits of the physical address for
> > metadata.  MKTME used several bits for an encryption KeyID.  TDX uses a
> > single bit in guests to communicate whether a physical page should be
> > protected by TDX as private memory (bit set to 0) or unprotected and
> > shared with the VMM (bit set to 1).
> > 
> > Add a helper, tdg_shared_mask() (bad name please fix it) to generate the
> 
> Initially we have used tdx_* prefix for the guest code. But when the code from
> host side got merged together, we came across many name conflicts.

Whatever the conflicts are, they are by no means an unsolvable problem.  I am
more than happy to end up with slightly verbose names in KVM if that's what it
takes to avoid "tdg".

> So to avoid such issues in future, we were asked not to use the "tdx_" prefix
> and our alternative choice was "tdg_".

Who asked you not to use tdx_?  More specifically, did that feedback come from a
maintainer (or anyone on-list), or was it an Intel-internal decision?

> Also, IMO, "tdg" prefix is more meaningful for guest code (Trusted Domain Guest)
> compared to "tdx" (Trusted Domain eXtensions). I know that it gets confusing
> when grepping for TDX related changes. But since these functions are only used
> inside arch/x86 it should not be too confusing.
> 
> Even if rename is requested, IMO, it is easier to do it in one patch over
> making changes in all the patches. So if it is required, we can do it later
> once these initial patches were merged.

Hell no, we are not merging known bad crud that requires useless churn to get
things right.