linux-kernel - Re: [PATCH 05/12] x86/mm: add INVLPGB support code

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Message-ID: <20250106181453.GBZ3wdnUpDfm_t6nvc@fat_crate.local>
Date: Mon, 6 Jan 2025 19:14:53 +0100
From: Borislav Petkov <bp@...en8.de>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Rik van Riel <riel@...riel.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org, kernel-team@...a.com,
	dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
	tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
	akpm@...ux-foundation.org, nadav.amit@...il.com,
	zhengqi.arch@...edance.com, linux-mm@...ck.org
Subject: Re: [PATCH 05/12] x86/mm: add INVLPGB support code

On Mon, Jan 06, 2025 at 08:50:27AM -0800, Dave Hansen wrote:
> There's some precedent for defining them all up front, like we did for
> invpcid_flush_*().
> 
> For INVPCID, there are four variants and two of them got used up front.
> But I get that it's a balancing act between having untested code that
> might bitrot and introducing helpers at a time when someone (Rik) is
> very likely to get all the variants coded up correctly.

That's just silly. We don't add all possible hw interface bits, defines etc,
when they're not going to be used. If we did, the kernel would be an unwieldy
mess of MSRs and their bits, unused insn opcodes and the like.

If someone wants to use them, someone can add them *when* they're needed - not
preemptively, in anticipation that *someone* *might* use them in the future.

Guys, I can't believe I'm actually arguing for something so obvious. 

:-\

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette