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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
	"the arch/x86 maintainers" <x86@kernel.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Andrew Lutomirski <luto@kernel.org>,
	Jiri Kosina <jkosina@suse.cz>,
	thomas.lendacky@amd.com, Josh Poimboeuf <jpoimboe@redhat.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	David Woodhouse <dwmw@amazon.co.uk>,
	Andi Kleen <ak@linux.intel.com>,
	dave.hansen@intel.com,
	Casey Schaufler <casey.schaufler@intel.com>,
	"Mallick, Asit K" <asit.k.mallick@intel.com>,
	"Van De Ven, Arjan" <arjan@linux.intel.com>,
	jcm@redhat.com, longman9394@gmail.com,
	Greg KH <gregkh@linuxfoundation.org>,
	david.c.stewart@intel.com, Kees Cook <keescook@chromium.org>,
	jason.w.brandt@intel.com
Subject: Re: [patch V2 27/28] x86/speculation: Add seccomp Spectre v2 user space protection mode
Date: Tue, 4 Dec 2018 09:20:52 -0800
Message-ID: <CAHk-=wj7h=eCrvEPuO_AJ2Y5T5akTQPs5cLA811O64wORf+NyQ@mail.gmail.com> (raw)
In-Reply-To: <f4b903ef-828c-0b05-29c6-6f71677d120d@linux.intel.com>

On Mon, Dec 3, 2018 at 5:38 PM Tim Chen <tim.c.chen@linux.intel.com> wrote:
>
> To make the usage of STIBP and its working principles clear,
> here are some additional explanations of STIBP from our Intel
> HW architects.  This should also help answer some of the questions
> from Thomas and others on STIBP's usages with IBPB and IBRS.
>
> Thanks.
>
> Tim
>
> ---
>
> STIBP
> ^^^^^
> Implementations of STIBP on existing Core-family processors (where STIBP
> functionality was added through a microcode update) work by disabling
> branch predictors that both:
>
>     1. Contain indirect branch predictions for both hardware threads, and
>     2. Do not contain a dedicated thread ID bit

Honestly, it still feels entirely misguided to me.

The above is not STIBP. It's just "disable IB". There's nothing "ST" about it.

So on processors where there is no thread ID bit (or per-thread
predictors), Intel simply SHOULD NOT EXPOSE this at all.

As it is, I refuse to call this shit "STIBP", because on current CPU's
that's simply a lie.

Being "technically correct" is not an excuse. It's just lying. I would
really hope that we restrict the lying to politicians, and not do it
in technical documentation.

               Linus

  parent reply index

Thread overview: 112+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-25 18:33 [patch V2 00/28] x86/speculation: Remedy the STIBP/IBPB overhead Thomas Gleixner
2018-11-25 18:33 ` [patch V2 01/28] x86/speculation: Update the TIF_SSBD comment Thomas Gleixner
2018-11-28 14:20   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:27   ` [patch V2 01/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 02/28] x86/speculation: Clean up spectre_v2_parse_cmdline() Thomas Gleixner
2018-11-28 14:20   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:28   ` [patch V2 02/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 03/28] x86/speculation: Remove unnecessary ret variable in cpu_show_common() Thomas Gleixner
2018-11-28 14:21   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:28   ` [patch V2 03/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 04/28] x86/speculation: Reorganize cpu_show_common() Thomas Gleixner
2018-11-26 15:08   ` Borislav Petkov
2018-11-28 14:22   ` [tip:x86/pti] x86/speculation: Move STIPB/IBPB string conditionals out of cpu_show_common() tip-bot for Tim Chen
2018-11-29 14:29   ` [patch V2 04/28] x86/speculation: Reorganize cpu_show_common() Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 05/28] x86/speculation: Disable STIBP when enhanced IBRS is in use Thomas Gleixner
2018-11-28 14:22   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:35   ` [patch V2 05/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 06/28] x86/speculation: Rename SSBD update functions Thomas Gleixner
2018-11-26 15:24   ` Borislav Petkov
2018-11-28 14:23   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:37   ` [patch V2 06/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 07/28] x86/speculation: Reorganize speculation control MSRs update Thomas Gleixner
2018-11-26 15:47   ` Borislav Petkov
2018-11-28 14:23   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-29 14:41   ` [patch V2 07/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 08/28] sched/smt: Make sched_smt_present track topology Thomas Gleixner
2018-11-28 14:24   ` [tip:x86/pti] " tip-bot for Peter Zijlstra (Intel)
2018-11-29 14:42   ` [patch V2 08/28] " Konrad Rzeszutek Wilk
2018-11-29 14:50     ` Konrad Rzeszutek Wilk
2018-11-29 15:48       ` Peter Zijlstra
2018-11-25 18:33 ` [patch V2 09/28] x86/Kconfig: Select SCHED_SMT if SMP enabled Thomas Gleixner
2018-11-28 14:24   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:44   ` [patch V2 09/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 10/28] sched/smt: Expose sched_smt_present static key Thomas Gleixner
2018-11-28 14:25   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-29 14:44   ` [patch V2 10/28] " Konrad Rzeszutek Wilk
2018-11-25 18:33 ` [patch V2 11/28] x86/speculation: Rework SMT state change Thomas Gleixner
2018-11-28 14:26   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 12/28] x86/l1tf: Show actual SMT state Thomas Gleixner
2018-11-28 14:26   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 13/28] x86/speculation: Reorder the spec_v2 code Thomas Gleixner
2018-11-26 22:21   ` Borislav Petkov
2018-11-28 14:27   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 14/28] x86/speculation: Mark string arrays const correctly Thomas Gleixner
2018-11-28 14:27   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 15/28] x86/speculataion: Mark command line parser data __initdata Thomas Gleixner
2018-11-28 14:28   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 16/28] x86/speculation: Unify conditional spectre v2 print functions Thomas Gleixner
2018-11-28 14:29   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 17/28] x86/speculation: Add command line control for indirect branch speculation Thomas Gleixner
2018-11-28 14:29   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 18/28] x86/speculation: Prepare for per task indirect branch speculation control Thomas Gleixner
2018-11-27 17:25   ` Lendacky, Thomas
2018-11-27 19:51     ` Tim Chen
2018-11-28  9:39       ` Thomas Gleixner
2018-11-27 20:39     ` Thomas Gleixner
2018-11-27 20:42       ` Thomas Gleixner
2018-11-27 21:52         ` Lendacky, Thomas
2018-11-28 14:30   ` [tip:x86/pti] " tip-bot for Tim Chen
2018-11-25 18:33 ` [patch V2 19/28] x86/process: Consolidate and simplify switch_to_xtra() code Thomas Gleixner
2018-11-26 18:30   ` Borislav Petkov
2018-11-28 14:30   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 20/28] x86/speculation: Avoid __switch_to_xtra() calls Thomas Gleixner
2018-11-28 14:31   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 21/28] x86/speculation: Prepare for conditional IBPB in switch_mm() Thomas Gleixner
2018-11-25 19:11   ` Thomas Gleixner
2018-11-25 20:53   ` Andi Kleen
2018-11-25 22:20     ` Thomas Gleixner
2018-11-25 23:04       ` Andy Lutomirski
2018-11-26  7:10         ` Thomas Gleixner
2018-11-26 13:36           ` Ingo Molnar
2018-11-26  3:07       ` Andi Kleen
2018-11-26  6:50         ` Thomas Gleixner
2018-11-28 14:31   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 22/28] ptrace: Remove unused ptrace_may_access_sched() and MODE_IBRS Thomas Gleixner
2018-11-28 14:32   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 23/28] x86/speculation: Split out TIF update Thomas Gleixner
2018-11-28 14:33   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 24/28] x86/speculation: Prepare arch_smt_update() for PRCTL mode Thomas Gleixner
2018-11-27 20:18   ` Lendacky, Thomas
2018-11-27 20:30     ` Thomas Gleixner
2018-11-27 21:20       ` Lendacky, Thomas
2018-11-28 14:34   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 25/28] x86/speculation: Add prctl() control for indirect branch speculation Thomas Gleixner
2018-11-28 14:34   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 26/28] x86/speculation: Enable prctl mode for spectre_v2_user Thomas Gleixner
2018-11-26  7:56   ` Dominik Brodowski
2018-11-28 14:35   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-25 18:33 ` [patch V2 27/28] x86/speculation: Add seccomp Spectre v2 user space protection mode Thomas Gleixner
2018-11-25 19:35   ` Randy Dunlap
2018-11-25 20:40   ` Linus Torvalds
2018-11-25 20:52     ` Jiri Kosina
2018-11-25 22:28     ` Thomas Gleixner
2018-11-26 13:30       ` Ingo Molnar
2018-11-26 20:48       ` Andrea Arcangeli
2018-11-26 20:58         ` Thomas Gleixner
2018-11-26 21:52           ` Lendacky, Thomas
2018-11-27  0:37             ` Tim Chen
2018-12-04  1:38     ` Tim Chen
2018-12-04  8:39       ` Jiri Kosina
2018-12-04  9:43         ` Arjan van de Ven
2018-12-04  9:46         ` Arjan van de Ven
2018-12-04 17:20       ` Linus Torvalds [this message]
2018-12-04 18:58         ` Tim Chen
2018-11-28 14:35   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-12-04 18:45   ` [patch V2 27/28] " Dave Hansen
2018-11-25 18:33 ` [patch V2 28/28] x86/speculation: Provide IBPB always command line options Thomas Gleixner
2018-11-28 14:36   ` [tip:x86/pti] " tip-bot for Thomas Gleixner
2018-11-26 13:37 ` [patch V2 00/28] x86/speculation: Remedy the STIBP/IBPB overhead Ingo Molnar
2018-11-28 14:24 ` Thomas Gleixner
2018-11-29 19:02   ` Tim Chen
2018-12-10 23:43 ` Pavel Machek

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