linux-kernel - Re: [PATCH 0/4] MSR: MSR: MSR Whitelist and Batch Introduction

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Message-ID: <20160229182047.GD3724@pd.tnic>
Date:	Mon, 29 Feb 2016 19:20:47 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	George Spelvin <linux@...izon.com>
Cc:	mcfadden8@...l.gov, a.p.zijlstra@...llo.nl, acme@...radead.org,
	ak@...ux.intel.com, andriy.shevchenko@...ux.intel.com,
	brgerst@...il.com, dan.j.williams@...el.com, dyoung@...hat.com,
	hpa@...or.com, jolsa@...hat.com, linux-kernel@...r.kernel.org,
	luto@...nel.org, mingo@...nel.org, mingo@...hat.com, pavel@....cz,
	tglx@...utronix.de, viro@...iv.linux.org.uk, x86@...nel.org,
	yu.c.chen@...el.com
Subject: Re: [PATCH 0/4] MSR: MSR: MSR Whitelist and Batch Introduction

On Mon, Feb 29, 2016 at 12:53:18PM -0500, George Spelvin wrote:
> I worry that this is this too ambitious a goal.  Who is volunteering
> to actually do this?

>From a quick look, the stuff in the examples was already in the rapl
driver.

> It takes quite a while to find a good OS-level abstraction (remember
> wakelocks?), and MSRs are the CPU architect's equivalent of ioctls.
> So they're a bit of a mess, and there will keep being new ones.

And yet you end up needing only a handful in most cases.

> I agree with you about anything that's going to see widespread use, but
> for specialized (apparently mostly HPC) use where the application really
> is heavily optimized for specific CPU models, perhaps dangerous-but-simple
> is good enough?

If it is that specialized, then it doesn't belong upstream.

> The proposed interface is simple and imposes very little maintenance
> burden on the kernel.  My main objection is that it's yet another
> special-case permission system.  Are we *sure* we'll never want to have
> to classes of users with different access rights?

The proposed interface is the wrong thing to do. There's no need to talk
about how simple and less of a burden it is.

The burden comes when people start complaining about strange issues and
we go and have to get a full MSR dump at the time the explosion happens
because some userspace tool went nuts and scribbled all over them. No
one wants to be on the receiving end of a bug report like this.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.