linux-kernel - Re: [PATCHv4 05/30] x86/tdx: Extend the confidential computing API to support TDX guests

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Date:   Fri, 25 Feb 2022 02:54:13 +0300
From:   "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        luto@...nel.org, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, aarcange@...hat.com,
        ak@...ux.intel.com, dan.j.williams@...el.com, david@...hat.com,
        hpa@...or.com, jgross@...e.com, jmattson@...gle.com,
        joro@...tes.org, jpoimboe@...hat.com, knsathya@...nel.org,
        pbonzini@...hat.com, sdeep@...are.com, seanjc@...gle.com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        thomas.lendacky@....com, brijesh.singh@....com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv4 05/30] x86/tdx: Extend the confidential computing API
 to support TDX guests

On Thu, Feb 24, 2022 at 09:54:16AM -0800, Dave Hansen wrote:
> 
> This left me wondering two things.  First, why this bothers storing
> 'gpa_width' when it's only used to generate a mask?  Why not just store
> the mask in the structure?

It was needed when tdx_shared_mask() was a thing. It takes a pair of
fresh eyes to break the inertia.

> Second, why have the global 'td_info' instead of just declaring it on
> the stack.  It is only used within a single function.  Having it on the
> stack is *REALLY* nice because the code ends up looking like:
> 
> 	struct foo foo;
> 	get_info(&foo);
> 	cc_set_bar(foo.bar);
> 
> The dependencies and scope are just stupidly obvious if you do that.

Okay, I will rework it with plain gpa_width on stack and get_info(&gpa_width);
Attributes will be needed after core enabling, so I will drop it from
here.

-- 
 Kirill A. Shutemov