linux-kernel - Re: [PATCH v2 01/29] x86: treewide: Introduce x86_vendor_amd_or

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Message-ID: <Z9iXMTIcz5xmqax1@gmail.com>
Date: Mon, 17 Mar 2025 22:42:09 +0100
From: Ingo Molnar <mingo@...nel.org>
To: "Ahmed S. Darwish" <darwi@...utronix.de>
Cc: Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Cooper <andrew.cooper3@...rix.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	John Ogness <john.ogness@...utronix.de>, x86@...nel.org,
	x86-cpuid@...ts.linux.dev, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 01/29] x86: treewide: Introduce
 x86_vendor_amd_or_hygon()


* Ahmed S. Darwish <darwi@...utronix.de> wrote:

> -	if (boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
> -	    boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)
> +	if (!x86_vendor_amd_or_hygon(boot_cpu_data.x86_vendor))
>  		return -ENODEV;

Could we just not do this?

The above vendor check may or may not be equivalent X86_FEATURE_ZEN1, 
which we could first assert via a single boot-time check:

	WARN_ON_ONCE(boot_cpu_has(X86_FEATURE_ZEN1) !=
			((boot_cpu_data.x86_vendor != X86_VENDOR_AMD &&
			  boot_cpu_data.x86_vendor != X86_VENDOR_HYGON)));

And then replace all the above with the much simpler construct of:

	if (!boot_cpu_has(X86_FEATURE_ZEN1))
		return -ENODEV;

But I'd suggest keeping this patch at the tail of the series, because 
if it regresses it would be easier to drop/revert.

Thanks,

	Ingo