linux-kernel - Re: [PATCH 3/3] x86/mm: Move _PAGE_BIT

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Message-ID: <hlcz5xsxko5aprmuzaodny45cpnfygz7axsn7muqpsbfhr56h2@kbiinejkqw6e>
Date: Thu, 23 Oct 2025 16:25:17 +0100
From: Kiryl Shutsemau <kas@...nel.org>
To: Dave Hansen <dave.hansen@...el.com>
Cc: Usama Arif <usamaarif642@...il.com>, dwmw@...zon.co.uk, 
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, 
	ardb@...nel.org, hpa@...or.com, x86@...nel.org, apopple@...dia.com, 
	thuth@...hat.com, nik.borisov@...e.com, linux-kernel@...r.kernel.org, 
	linux-efi@...r.kernel.org, kernel-team@...a.com, 
	Michael van der Westhuizen <rmikey@...a.com>, Tobias Fleig <tfleig@...a.com>
Subject: Re: [PATCH 3/3] x86/mm: Move _PAGE_BIT_NOPTISHADOW from bit 58 to
 bit 9

On Thu, Oct 23, 2025 at 08:12:32AM -0700, Dave Hansen wrote:
> On 10/23/25 07:24, Kiryl Shutsemau wrote:
> > The last patch allows us to only update the kernel that has 5-level
> > paging enabled, making it much easier logistically.
> > 
> > The fix seems trivial, and I don't see any downsides.
> 
> What I'm hearing is: Please change mainline so $COMPANY can do fewer
> backports.

Or you can read it as: without the fix 5-level paging deployment is
harder.

One other point is that crashkernels tend to be older and update less
frequently than the main kernel. And one would only discover that
crashdump doesn't work when the crash happens.

> Yeah, it's pretty trivial. But I'm worried about the precedent, and I'm
> worried that the change doesn't do a thing for mainline. It's pure
> churn. Churn has inherent downsides.

You don't consider kexec to older kernels useful for mainline?

> I'd urge you to kick this out of the series and focus on the bug fixes
> that are unambiguously good for everyone. Let's have a nice big flamewar
> in another thread.

Oh, well... Okay.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov