Date: Mon, 29 Jun 2015 08:42:43 +0200
From: Ingo Molnar <mingo@kernel.org>
To: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Prarit Bhargava <prarit@redhat.com>, Andy Lutomirski <luto@amacapital.net>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "H. Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, X86 ML <x86@kernel.org>,
        Len Brown <len.brown@intel.com>,
        Dasaratharaman Chandramouli 
	<dasaratharaman.chandramouli@intel.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Borislav Petkov <bp@alien8.de>, Andy Lutomirski <luto@kernel.org>,
        Denys Vlasenko <dvlasenk@redhat.com>, Brian Gerst <brgerst@gmail.com>,
        Arnaldo Carvalho de Melo <acme@infradead.org>
Subject: Re: [PATCH] x86, msr: Allow read access to /dev/cpu/X/msr
Message-ID: <20150629064243.GB16251@gmail.com>
References: <1435341131-3279-1-git-send-email-prarit@redhat.com>
 <20150627083354.GA12834@gmail.com>
 <20150627083921.GA13074@gmail.com>
 <CALCETrXpiMWwiAfbxcKTDYCewrwq-UTwLV+xXTxdOkd+B3G-OQ@mail.gmail.com>
 <559005DD.3070003@redhat.com>
 <20150628151049.GB20989@khazad-dum.debian.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20150628151049.GB20989@khazad-dum.debian.net>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1073
Lines: 31


* Henrique de Moraes Holschuh <hmh@hmh.eng.br> wrote:

> On Sun, 28 Jun 2015, Prarit Bhargava wrote:
>
> > Is it easier to blacklist MSRs we don't want generally exposed, or only expose 
> > the ones that we think are safe?  That's sort of a devil's advocate sort of 
> > question ;) and I'm wondering what the shorter list is.
> 
> The only way to make MSR access safe is to allow it only by whitelisting. The 
> x86 platform restricts all MSR access to ring 0 for a damn good reason.

Exactly.

We also want to document them along the way: just exposing all doesn't achieve 
that.

> Also, such a whitelist would most likely need to be vendor and model-aware, and 
> to differentiate "allow reads" from "allow writes"...

Initially it should only allow reads - which I believe fully meets turbostat's 
needs.

Thanks,

	Ingo
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/