linux-kernel - RE: [PATCH] x86/split_lock: Enable the split lock detect feature on Raptor Lake P and Alder Lake N CPUs

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Message-ID: <aa0ee519f6dc49f9b866abb438bde1e1@AcuMS.aculab.com>
Date:   Sat, 2 Jul 2022 10:32:33 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Dave Hansen' <dave.hansen@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        "Dave Hansen" <dave.hansen@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>,
        "Tony Luck" <tony.luck@...el.com>
CC:     x86 <x86@...nel.org>, linux-kernel <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] x86/split_lock: Enable the split lock detect feature on
 Raptor Lake P and Alder Lake N CPUs

From: Dave Hansen
> Sent: 01 July 2022 15:20
> 
> On 7/1/22 06:19, Fenghua Yu wrote:
> > These CPU models support the split lock detect feature. Add them to
> > the x86_cpu_ids match table.
> 
> When is there going to be architectural detection for this feature?  Or,
> is the plan to just keep adding CPUs to this table as they are available.

I saw that as well, it really doesn't scale at all.

Isn't it usual for the flag to not be settable on old cpu?

In any case the flag could be set and then a 'split lock'
transfer and see if it faults.

OTOH why bother with the test?
Unless you want to report that the 'split lock' detection
doesn't work?

Or did Intel really screw this up and use a flag that has
some other undesirable effect on (at least some) older cpu.

	David

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