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From: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
To: Borislav Petkov <bp@alien8.de>, Sultan Alsawaf <sultan@kerneltoast.com>
Cc: "Jason A. Donenfeld" <Jason@zx2c4.com>,
	kitsunyan <kitsunyan@airmail.cc>,
	"Brown, Len" <len.brown@intel.com>, X86 ML <x86@kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH] x86/msr: do not warn on writes to OC_MAILBOX
Date: Tue, 08 Sep 2020 18:02:05 -0700	[thread overview]
Message-ID: <fa447f6b7c7f03cc0c55573d5736889cee81a1e6.camel@linux.intel.com> (raw)
In-Reply-To: <20200908193029.GM25236@zn.tnic>

On Tue, 2020-09-08 at 21:30 +0200, Borislav Petkov wrote:
> On Tue, Sep 08, 2020 at 12:18:38PM -0700, Sultan Alsawaf wrote:
> > I'd like to point out that on Intel's recent 14nm parts,
> > undervolting
> > is not so much for squeezing every last drop of performance out of
> > the
> > SoC as it is for necessity.
> 
> <snip interesting examples>
> 
> Sounds to me that this undervolting functionality should be part of
> the kernel and happen automatically. I have no clue, though, whether
> people who do it, just get lucky and undervolting doesn't cause any
> other hardware issues, or there's a real reason for this power
> madness
> and if not done, power-related failures happen only on some boxes so
> they decided to do them on all.
> 
> Or maybe BIOS is nuts, which is not a stretch.
> 
The whole OC is based on experiments to come to correct values. This
depends on whole system design not just CPUs.
https://www.intel.com/content/www/us/en/gaming/resources/how-to-overclock.html
It warns about system stability.

> Srinivas, what's the story here?
I checked and there is no public spec. There are several mailbox
commands with version dependent on the processor.

The actual OC mailbox implementation itself is implemented in Linux in
intel_turbo_max_3 driver. So that is public.
So someone can develop a driver and provide some sysfs to send mailbox
commands, but kernel can't validate commands which can cause any
security or stability issues. Not sure if this is acceptable standard.
I don't think there is any precedent of creating such blind sysfs
entries.


Thanks,
Srinivas


  parent reply	other threads:[~2020-09-09  1:02 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-07  9:48 [PATCH] x86/msr: do not warn on writes to OC_MAILBOX Jason A. Donenfeld
2020-09-07 10:06 ` Borislav Petkov
2020-09-07 10:46   ` Jason A. Donenfeld
2020-09-07 11:11     ` Borislav Petkov
2020-09-07 11:15       ` Jason A. Donenfeld
2020-09-07 11:23         ` Borislav Petkov
2020-09-08 17:10   ` Srinivas Pandruvada
2020-09-08 17:12     ` Jason A. Donenfeld
2020-09-08 17:25       ` Borislav Petkov
2020-09-08 17:29         ` Jason A. Donenfeld
2020-09-08 17:36           ` Borislav Petkov
2020-09-08 17:42             ` Jason A. Donenfeld
2020-09-08 18:01               ` Borislav Petkov
2020-09-08 19:07                 ` Jason A. Donenfeld
2020-09-08 19:18                 ` Sultan Alsawaf
2020-09-08 19:30                   ` Borislav Petkov
2020-09-08 20:35                     ` Andy Lutomirski
2020-09-08 22:32                       ` Matthew Garrett
2020-09-09 23:56                         ` Andy Lutomirski
2020-09-09  1:02                     ` Srinivas Pandruvada [this message]
2020-09-10  0:08                       ` Andy Lutomirski
2020-10-19 17:15                       ` Borislav Petkov
2020-10-20 17:21                         ` Srinivas Pandruvada
2020-10-20 17:47                           ` Borislav Petkov
2020-10-20 18:40                             ` Srinivas Pandruvada
2020-10-20 19:40                               ` Dave Hansen
2020-10-21 13:11                                 ` Srinivas Pandruvada
2020-10-22 19:28                                   ` Borislav Petkov
2020-10-21 13:24                           ` Peter Zijlstra
2020-09-08 17:31     ` Borislav Petkov

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