linux-kernel - Re: [patch v3 2/7] x86/smp: Dont access non-existing CPUID leaf

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Message-ID: <20230620082023.GTZJFhRxji7SHvvmdk@fat_crate.local>
Date:   Tue, 20 Jun 2023 10:20:23 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
        Mario Limonciello <mario.limonciello@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tony Battersby <tonyb@...ernetics.com>,
        Ashok Raj <ashok.raj@...ux.intel.com>,
        Tony Luck <tony.luck@...el.com>,
        Arjan van de Veen <arjan@...ux.intel.com>,
        Eric Biederman <ebiederm@...ssion.com>
Subject: Re: [patch v3 2/7] x86/smp: Dont access non-existing CPUID leaf

On Thu, Jun 15, 2023 at 10:33:52PM +0200, Thomas Gleixner wrote:

> Subject: Re: [patch v3 2/7] x86/smp: Dont access non-existing CPUID leaf

"Do not access a non-existing... "

> From: Tony Battersby <tonyb@...ernetics.com>
> 
> stop_this_cpu() tests CPUID leaf 0x8000001f::EAX unconditionally. CPUs
> return the content of the highest supported leaf when a non-existing leaf
> is read.

This should be:

"On Intel, querying an invalid extended CPUID leaf returns the values of the
maximum basic CPUID leaf. On AMD, invalid CPUID leafs return zeros."

Other than that:

Reviewed-by: Borislav Petkov (AMD) <bp@...en8.de>

-- 
Regards/Gruss,
    Boris.

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