linux-kernel - Re: [PATCH] x86: coco: mark cc_mask as __maybe

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Message-Id: <f034fd64-41e9-45fd-a58f-41dae347307c@app.fastmail.com>
Date: Mon, 10 Mar 2025 14:50:18 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Ingo Molnar" <mingo@...nel.org>, "Arnd Bergmann" <arnd@...nel.org>
Cc: "Thomas Gleixner" <tglx@...utronix.de>, "Ingo Molnar" <mingo@...hat.com>,
 "Borislav Petkov" <bp@...en8.de>,
 "Dave Hansen" <dave.hansen@...ux.intel.com>, x86@...nel.org,
 "Kuppuswamy Sathyanarayanan" <sathyanarayanan.kuppuswamy@...ux.intel.com>,
 "Rick Edgecombe" <rick.p.edgecombe@...el.com>,
 "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
 "Tom Lendacky" <thomas.lendacky@....com>, "H. Peter Anvin" <hpa@...or.com>,
 "Jason A . Donenfeld" <Jason@...c4.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86: coco: mark cc_mask as __maybe_unused

On Wed, Mar 5, 2025, at 11:44, Ingo Molnar wrote:
> * Arnd Bergmann <arnd@...nel.org> wrote:
>
>> @@ -25,7 +25,7 @@ u64 cc_mkdec(u64 val);
>>  void cc_random_init(void);
>>  #else
>>  #define cc_vendor (CC_VENDOR_NONE)
>> -static const u64 cc_mask = 0;
>> +static const __maybe_unused u64 cc_mask = 0;
>
> So I detest __maybe_unused with a vengeance: the 'maybe' unnecessarily 
> inserts uncertainty & probability language into the text, while there's 
> nothing uncertain about this interface or the code. Why cannot the 
> compiler figure it out?

Right, I'm also trying to remove a lot of the __maybe_unused
annotations in places like power management and device_id tables
where we now have better solutions in place.

> Anyway, I'd suggest we change direct usage of cc_mask to a 
> get_cc_mask() inline function instead, this will resolve the warning, 
> plus it avoids some messy looking variable shadowing in tdx.c AFAICS:
>
>   arch/x86/coco/tdx/tdx.c:static void tdx_setup(u64 *cc_mask)

I've sent a v2 now.

      Arnd