linux-kernel - Re: [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the CPUID instruction.

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Message-ID: <20160912182519.GA23180@khazad-dum.debian.net>
Date:   Mon, 12 Sep 2016 15:25:19 -0300
From:   Henrique de Moraes Holschuh <hmh@....eng.br>
To:     Andi Kleen <andi@...stfloor.org>
Cc:     Kyle Huey <khuey@...ehuey.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the
 CPUID instruction.

On Mon, 12 Sep 2016, Andi Kleen wrote:
> The cpuid char driver does this, other code may too.

Such as anything that calls sync_core().

That includes processor hotplug paths, and who knows what else...

> You probably would need to protect these CPUIDs with an exception
> handler that temporarily disables this bit and retries.

Better time that MSR access first.  Hopefully, it is fast enough for
that.

-- 
  Henrique Holschuh