linux-kernel - Re: [PATCH] x86/msr: do not warn on writes to OC

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Message-ID: <CAHmME9pVO01mj8vgKPEX7a6pZDRSfX62e2Ow8R=L79hLSJoaMA@mail.gmail.com>
Date:   Tue, 8 Sep 2020 19:42:12 +0200
From:   "Jason A. Donenfeld" <Jason@...c4.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        kitsunyan <kitsunyan@...mail.cc>,
        "Brown, Len" <len.brown@...el.com>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sultan Alsawaf <sultan@...neltoast.com>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX

On Tue, Sep 8, 2020 at 7:36 PM Borislav Petkov <bp@...en8.de> wrote:
>
> On Tue, Sep 08, 2020 at 07:29:11PM +0200, Jason A. Donenfeld wrote:
> > Well that's not cool.
>
> So you're saying that if someone wants to kill its box by poking at that
> MSR, we should just let her/him?
>
> If anything, I think that a BIG FAT WARNING at least would make sense.

Are you prepared to track down all the MSRs that might maybe do
something naughty?

After determining optimal voltages, people have systemd running
intel-undervolt for them. It becomes part of the normal system
configuration, is applied all the time, and after figuring it out
once, users forget they ever had enabled it, except when observing
that their laptop works better than it originally did.

Does `dd` warn when you run `dd if=/dev/zero of=/dev/sda`?

> Now, if there were a proper interface which would allow only valid
> commands, now that would be optimal...

Probably not possible. Optimal values are related to the "silicon
lottery" that occurs when you buy a new CPU. Different optimal values
for different individual chips.