linux-kernel - Re: [PATCHv7.1 02/30] x86/tdx: Provide common base for SEAMCALL and TDCALL C wrappers

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Date:   Mon, 4 Apr 2022 17:01:27 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Kai Huang <kai.huang@...el.com>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        bp@...en8.de
Cc:     aarcange@...hat.com, ak@...ux.intel.com, brijesh.singh@....com,
        dan.j.williams@...el.com, dave.hansen@...ux.intel.com,
        david@...hat.com, hpa@...or.com, jgross@...e.com,
        jmattson@...gle.com, joro@...tes.org, jpoimboe@...hat.com,
        knsathya@...nel.org, linux-kernel@...r.kernel.org, luto@...nel.org,
        mingo@...hat.com, pbonzini@...hat.com, peterz@...radead.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com, sdeep@...are.com,
        seanjc@...gle.com, tglx@...utronix.de, thomas.lendacky@....com,
        tony.luck@...el.com, vkuznets@...hat.com, wanpengli@...cent.com,
        x86@...nel.org
Subject: Re: [PATCHv7.1 02/30] x86/tdx: Provide common base for SEAMCALL and
 TDCALL C wrappers

On 4/4/22 16:35, Kai Huang wrote:
> Both error code formats defined by P-SEAMLDR and TDX module has some reserved
> bits which will never be set to 1.  I think we can just add a simple comment
> explaining that and choose a value which has 1 set for those reserved bits (even
> doesn't have to be -1). For example:
> 
> 	/*
> 	 * Use -1ULL which will never conflict with any actual error code
> 	 * returned by both the P-SEAMLDR and the TDX module to represent
> 	 * VMfailInvalid.  Both error code definitions defined by the
> 	 * P-SEAMLDR and the TDX module have some reserved bits which will
> 	 * never be set to 1.
> 	 */
> 	#define TDX_SEAMCALL_VMFAILINVALID	GENMASK_ULL(63, 0)

The vague "some reserved bits" magic works for exactly *one* error code.
 If you ever want to make it two, then you subject some some poor future
dope to a trip to TDX documentation purgatory.

All I'm asking is that this code stand on its own.  Just declare what
the *ACTUAL* reserved bits are.  Not some vague reference to "some
bits".  There are *REAL* documented bits.  Use them, please.