From: Thomas Gleixner <tglx@linutronix.de>
To: Ingo Molnar <mingo@kernel.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
Linus Torvalds <torvalds@linuxfoundation.org>,
x86@kernel.org, Peter Zijlstra <peterz@infradead.org>,
Borislav Petkov <bp@alien8.de>,
David Woodhouse <dwmw@amazon.co.uk>,
Tim Chen <tim.c.chen@linux.intel.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Andi Kleen <ak@linux.intel.com>,
Greg KH <gregkh@linuxfoundation.org>,
Dave Hansen <dave.hansen@intel.com>,
Andy Lutomirski <luto@kernel.org>,
Arjan Van De Ven <arjan.van.de.ven@intel.com>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [patch RFC 4/5] x86/cpufeatures: Detect Speculation control feature
Date: Wed, 10 Jan 2018 12:06:06 +0100 (CET) [thread overview]
Message-ID: <alpine.DEB.2.20.1801101204250.1919@nanos> (raw)
In-Reply-To: <20180110063211.z6w55gwxm5szmt2l@gmail.com>
On Wed, 10 Jan 2018, Ingo Molnar wrote:
> > If CPUID(7).RDX[26] is set then MSR_IA32_SPEC_CTRL (0x48) is available and
> > bit 0 of that MSR controls whether Indirect Branch Speculation is
> > restricted or not. The control bit is named IBRS (Indirect Branch
> > Restricted Speculation). The IBSR bit can be unconditionally set to 1
> > without clearing it before.
>
> Argh for inverted logic: why was the control bit defined for a _negated_ value,
> i.e. why does '0' mean "don't don't speculate"?
>
> And yes, I know what's behind it: this way 'IBRS' can be called a 'mitigation
> feature' that can be 'enabled', instead of calling it a 'broken CPU feature
> feature' that has to be disabled ...
>
> That's nonsense that causes confusion to no end:
Yes, it's horrible and on my todo list to clean that up at least on any
layer which is above the pure MSR definition level, which we can't change.
The steam blasting of that mess is not even halfways done.
Thanks,
tglx
next prev parent reply other threads:[~2018-01-10 11:06 UTC|newest]
Thread overview: 64+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-01-10 1:06 [patch RFC 0/5] x86/spectre_v2: Initial integration of IBRS into the spectre_v2 mechanics Thomas Gleixner
2018-01-10 1:06 ` [patch RFC 1/5] x86/CPU: Sync CPU feature flags late Thomas Gleixner
2018-01-10 1:37 ` Dave Hansen
2018-01-10 1:39 ` Van De Ven, Arjan
2018-01-10 1:47 ` Thomas Gleixner
2018-01-10 2:57 ` Andy Lutomirski
2018-01-10 11:02 ` Thomas Gleixner
2018-01-10 1:44 ` Thomas Gleixner
2018-01-10 6:20 ` Ingo Molnar
2018-01-10 11:33 ` Borislav Petkov
2018-01-10 12:38 ` Thomas Gleixner
2018-01-10 1:06 ` [patch RFC 2/5] x86/spectre: Simplify spectre code a bit Thomas Gleixner
2018-01-10 6:22 ` Ingo Molnar
2018-01-10 1:06 ` [patch RFC 3/5] x86/spectre: Prepare for IBRS selection Thomas Gleixner
2018-01-10 1:51 ` Dave Hansen
2018-01-10 1:06 ` [patch RFC 4/5] x86/cpufeatures: Detect Speculation control feature Thomas Gleixner
2018-01-10 6:32 ` Ingo Molnar
2018-01-10 11:06 ` Thomas Gleixner [this message]
2018-01-10 1:06 ` [patch RFC 5/5] x86/speculation: Add basic speculation control code Thomas Gleixner
2018-01-10 2:02 ` Dave Hansen
2018-01-10 4:11 ` Justin Forbes
2018-01-10 9:22 ` Peter Zijlstra
2018-01-10 9:27 ` David Woodhouse
2018-01-10 10:03 ` Peter Zijlstra
2018-01-10 11:22 ` David Woodhouse
2018-01-10 11:41 ` Thomas Gleixner
2018-01-10 11:45 ` Peter Zijlstra
2018-01-10 11:54 ` Andrea Arcangeli
2018-01-10 11:58 ` David Woodhouse
2018-01-10 12:01 ` Andrea Arcangeli
2018-01-10 12:07 ` Andrea Arcangeli
2018-01-10 12:12 ` David Woodhouse
2018-01-10 12:20 ` Andrea Arcangeli
2018-01-10 12:27 ` Andrea Arcangeli
2018-01-10 13:42 ` Van De Ven, Arjan
2018-01-10 12:09 ` David Woodhouse
2018-01-10 12:17 ` Andrea Arcangeli
2018-01-10 12:29 ` David Woodhouse
2018-01-10 12:41 ` Andrea Arcangeli
2018-01-10 12:47 ` Jiri Kosina
2018-01-10 12:51 ` David Woodhouse
2018-01-10 13:02 ` Andrea Arcangeli
2018-01-10 13:05 ` Andrea Arcangeli
2018-01-10 13:10 ` Andrea Arcangeli
2018-01-10 13:12 ` Andrea Arcangeli
2018-01-10 12:57 ` Andrea Arcangeli
2018-01-10 13:07 ` David Woodhouse
2018-01-10 13:45 ` Van De Ven, Arjan
2018-01-10 13:52 ` Andrea Arcangeli
2018-01-10 13:53 ` Van De Ven, Arjan
2018-01-10 21:35 ` Tim Chen
2018-01-10 22:13 ` Andrea Arcangeli
2018-01-10 13:46 ` Thomas Gleixner
2018-01-10 13:51 ` Van De Ven, Arjan
2018-01-10 13:53 ` Thomas Gleixner
2018-01-10 13:58 ` David Woodhouse
2018-01-10 14:10 ` Andrea Arcangeli
2018-01-10 14:14 ` Van De Ven, Arjan
2018-01-10 14:59 ` Dave Hansen
2018-01-10 15:13 ` Andrea Arcangeli
2018-01-10 15:24 ` David Woodhouse
2018-01-10 15:47 ` Andrea Arcangeli
2018-01-10 15:56 ` David Woodhouse
2018-01-10 13:10 ` Jiri Kosina
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