linux-kernel - Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff

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Date:   Tue, 25 Apr 2023 13:03:22 -0700
From:   Dave Hansen <dave.hansen@...el.com>
To:     Tony Battersby <tonyb@...ernetics.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org
Cc:     "H. Peter Anvin" <hpa@...or.com>,
        Mario Limonciello <mario.limonciello@....com>,
        Tom Lendacky <thomas.lendacky@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC] x86/cpu: fix intermittent lockup on poweroff

On 4/25/23 12:26, Tony Battersby wrote:
> -	if (cpuid_eax(0x8000001f) & BIT(0))
> +	if (c->extended_cpuid_level >= 0x8000001f &&
> +	    (cpuid_eax(0x8000001f) & BIT(0)))
>  		native_wbinvd();

Oh, so the existing code is running into the

> If a value entered for CPUID.EAX is higher than the maximum input
> value for basic or extended function for that processor then the data
> for the highest basic information leaf is returned
behavior.  It's basically looking at BIT(0) of some random extended
leaf.  Probably 0x80000008 based on your 'cpuid -r' output.