linux-kernel - Re: [PATCH v7 9/9] x86/startup_64: Drop global variables keeping track of LA57 state

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Date: Sat, 2 Mar 2024 16:17:20 +0100
From: Borislav Petkov <bp@...en8.de>
To: Ard Biesheuvel <ardb@...nel.org>
Cc: linux-kernel@...r.kernel.org, Kevin Loughlin <kevinloughlin@...gle.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	Dionna Glaze <dionnaglaze@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>, Brian Gerst <brgerst@...il.com>
Subject: Re: [PATCH v7 9/9] x86/startup_64: Drop global variables keeping
 track of LA57 state

On Sat, Mar 02, 2024 at 12:55:14AM +0100, Ard Biesheuvel wrote:
> Today, pgtable_l5_enabled() is used in many places, most of which
> resolve to cpu_feature_enabled(), and I don't think you are suggesting
> to replace all of those with a variable load, right?

pgtable_l5_enabled() is the odd one out, special thing which should
have been cpu_feature_enabled() as latter is the default interface we
use to query what features the CPU supports. But 5level got done long
ago and we hadn't decided upon cpu_feature_enabled() back then.

So should we replace it with it?

Yap, eventually.

> So that means we'll have to stick with early and late variants of
> pgtable_l5_enabled() like we have today,

I don't mind at all if we had a

	early_pgtable_l5_enabled()

which does the RIP_REL_REF() thing and it should be used only in 1:1
mapping code and the late stuff should start to get replaced with
cpu_feature_enabled() until pgtable_l5_enabled() is completely gone.

And then we even see whether we can opencode the handful places.

> and we should just drop this patch instead - I put it at the end of
> the series for a reason.

Yeah, we can leave that one aside for now but use it to start a cleanup
series.

If you're bored and feel like doing it, be my guest but for the next
cycle. Or I'll put it on my evergrowing TODO and get to it eventually.

For now, lemme test your set without this one and see whether we can
queue them even now.

Thx.

-- 
Regards/Gruss,
    Boris.

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