linux-kernel - Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support unconditional

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Message-ID: <20250516155649.GFaCdgQa7sX75vOLSm@fat_crate.local>
Date: Fri, 16 May 2025 17:56:49 +0200
From: Borislav Petkov <bp@...en8.de>
To: Ingo Molnar <mingo@...nel.org>
Cc: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ard Biesheuvel <ardb@...nel.org>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	Kieran Bingham <kbingham@...nel.org>,
	Michael Roth <michael.roth@....com>,
	Rick Edgecombe <rick.p.edgecombe@...el.com>,
	Brijesh Singh <brijesh.singh@....com>,
	Sandipan Das <sandipan.das@....com>,
	Juergen Gross <jgross@...e.com>,
	Tom Lendacky <thomas.lendacky@....com>,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv2 3/3] x86/64/mm: Make 5-level paging support
 unconditional

On Fri, May 16, 2025 at 05:46:51PM +0200, Ingo Molnar wrote:
> 
> * Borislav Petkov <bp@...en8.de> wrote:
> 
> > On Fri, May 16, 2025 at 12:15:33PM +0300, Kirill A. Shutemov wrote:
> > > @@ -173,10 +173,10 @@ For example, when an old kernel is running on new hardware.
> > >  The kernel disabled support for it at compile-time
> > >  --------------------------------------------------
> > >  
> > > -For example, if 5-level-paging is not enabled when building (i.e.,
> > > -CONFIG_X86_5LEVEL is not selected) the flag "la57" will not show up [#f1]_.
> > > +For example, if Linear Address Masking (LAM) is not enabled when building (i.e.,
> > > +CONFIG_ADDRESS_MASKING is not selected) the flag "lam" will not show up.
> > >  Even though the feature will still be detected via CPUID, the kernel disables
> > > -it by clearing via setup_clear_cpu_cap(X86_FEATURE_LA57).
> > > +it by clearing via setup_clear_cpu_cap(X86_FEATURE_LAM).
> > 
> > LOL, good one.
> > 
> > The rest looks nice and good to me. And FWIW, it boots fine on my Zen5 with
> > 5lvl enabled.
> > 
> > Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>

Bah, and I thought I'm replying to v3. :-\

Anyway...

> What's your preference on timing? v6.17 or v6.16?

Right, here's what I'm thinking:

* Kirill's patches would simplify Ard's cleanup a bit

* The 4th one: Kirill A. Shutemov ( :  85|) ├─>[PATCHv3 4/4] x86/paravirt: Restrict PARAVIRT_XXL to 64-bit only

looks ok too.

So, I don't see anything speaking against queueing them *now* for the upcoming
merge window, I am testing the tip lineup on a daily basis this and next week
and if it all looks good, we could probably send them.

If not, we delay.

And if there's other issues which get detected later, during the 6.16-rc
phase, we revert.

So we have an exit route from each scenario.

So I guess let's...

Unless I'm missing an aspect.

Thx.

-- 
Regards/Gruss,
    Boris.

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