linux-kernel - Re: [PATCH] x86/CPU/AMD: Perform function calls post ZEN feature check regardless

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Message-ID: <20250812213718.GIaJu0DgbRbBq2mfDY@fat_crate.local>
Date: Tue, 12 Aug 2025 23:37:18 +0200
From: Borislav Petkov <bp@...en8.de>
To: Tom Lendacky <thomas.lendacky@....com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/CPU/AMD: Perform function calls post ZEN feature
 check regardless

On Wed, Jul 23, 2025 at 12:01:06PM -0500, Tom Lendacky wrote:
> Currently, if a ZEN family/model is not recognized in bsp_init_amd(), then
> function calls after the family/model check are skipped. This can prevent
> older kernels from enabling features on newer hardware, e.g., unrecognized
> new hardware won't enable SEV-SNP because bsp_determine_snp() is skipped.

bsp_determine_snp() relies partly on the family detection.

If all you care is calling it even without family detection, why don't you
pull it up, check c->x86 and be done with it?

But even then: we don't really care about older kernels on newer hardware
- that's why they get backports. We don't really think about backporting when
working upstream. Frankly...

So I'm sceptical about this.

-- 
Regards/Gruss,
    Boris.

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