linux-kernel - Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by kernel parameter

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Message-ID: <20191122100856.GX4114@hirez.programming.kicks-ass.net>
Date:   Fri, 22 Nov 2019 11:08:56 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Luck, Tony" <tony.luck@...el.com>
Cc:     Ingo Molnar <mingo@...nel.org>, Fenghua Yu <fenghua.yu@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        H Peter Anvin <hpa@...or.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Ravi V Shankar <ravi.v.shankar@...el.com>,
        linux-kernel <linux-kernel@...r.kernel.org>, x86 <x86@...nel.org>
Subject: Re: [PATCH v10 6/6] x86/split_lock: Enable split lock detection by
 kernel parameter

On Thu, Nov 21, 2019 at 01:51:26PM -0800, Luck, Tony wrote:
> On Thu, Nov 21, 2019 at 02:15:22PM +0100, Peter Zijlstra wrote:
> > Also, just to remind everyone why we really want this. Split lock is a
> > potent, unprivileged, DoS vector.
> 
> So how much do we "really want this"?
> 
> It's been 543 days since the first version of this patch was
> posted. We've made exactly zero progress.

Well, I was thinking we were getting there, but then, all of 58 days ago
you discovered the MSR was per core, which is rather fundamental and
would've been rather useful to know at v1.

  http://lkml.kernel.org/r/20190925180931.GG31852@linux.intel.com

So that is ~485 days wasted because we didn't know how the hardware
actually worked. I'm not thinking that's on us.


Also, talk like:

> I believe Intel real time team guarantees to deliever a split lock FREE
> BIOS/EFI/firmware to their real time users.

is fundamentally misguided. Everybody who buys a chip (with this on) is
a potential real-time customer.