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

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Date:   Tue, 25 Apr 2023 23:06:54 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Dave Hansen <dave.hansen@...el.com>
Cc:     Tony Battersby <tonyb@...ernetics.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "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 Tue, Apr 25, 2023 at 01:34:48PM -0700, Dave Hansen wrote:
> >    0x0000000b 0x00: eax=0x00000001 ebx=0x00000002 ecx=0x00000100 edx=0x00000000
> 
> which does have BIT(0) set.

Yeah, or the last basic leaf

  0x0000000b 0x01: eax=0x00000005 ebx=0x0000000c ecx=0x00000201 edx=0x00000000

but that one has bit 0 set too, so yeah, patch is correct. I'll queue it
after -rc1.

But Tony, please change your commit message to say something like this:

"Check the maximum supported extended CPUID level because on Intel,
querying an invalid extended CPUID leaf returns the values of the
maximum basic CPUID leaf and if bit  0 in EAX is set, the check falsely
evaluates to true and WBINVD is wrongly executed where it shouldn't."

Thx.

-- 
Regards/Gruss,
    Boris.

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