linux-kernel - Re: [PATCHv4 03/30] x86/tdx: Provide common base for SEAMCALL and TDCALL C wrappers

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Date:   Fri, 25 Feb 2022 08:12:18 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.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 03/30] x86/tdx: Provide common base for SEAMCALL and
 TDCALL C wrappers

> Bit 63 also has to be set as it represents error (0 is success with
> possible warning).
> 
> Bit 62 indicates if the error is recoverable. (0 is recoverable)
> 
> Bits 61:48 are reserved and must be 0. For this reason -1UL is not right.
> 
> Bits 47:40 are class.
> 
> Bits below that are up to grub.
> 
> See Table 17.6 of TDX module 1.0 spec.
> 
> So we can use 
> 
> #define TDX_SW_CLASS(code)		((code) | GENMASK_ULL(40, 47))
> #define TDX_ERROR(code)			((code) | (1UL << 63))
> #define TDX_SEAMCALL_VMFAILINVALID	TDX_ERROR(TDX_SW_CLASS(0xFFFF0000ULL))
> 
> But it looks silly to me. It brings more confusion than solves.

Passing 'code' is kinda silly now that I look at it.  But, this:

#define TDX_ERROR			(1UL << 63)
#define TDX_SW_ERROR 			(TDX_ERROR | GENMASK_ULL(40, 47))
#define TDX_SEAMCALL_VMFAILINVALID	(TDX_SW_ERROR | 0xFFFF0000ULL)

Actually gives you a chance in hell of connecting this code back to the
spec.