All of lore.kernel.org
 help / color / mirror / Atom feed
From: Andrea Arcangeli <aarcange@redhat.com>
To: "Van De Ven, Arjan" <arjan.van.de.ven@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	"Hansen, Dave" <dave.hansen@intel.com>,
	Peter Zijlstra <peterz@infradead.org>,
	David Woodhouse <dwmw2@infradead.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	LKML <linux-kernel@vger.kernel.org>,
	"Raj, Ashok" <ashok.raj@intel.com>,
	Tim Chen <tim.c.chen@linux.intel.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Greg KH <gregkh@linuxfoundation.org>,
	Andi Kleen <ak@linux.intel.com>,
	"Williams, Dan J" <dan.j.williams@intel.com>,
	"Nakajima, Jun" <jun.nakajima@intel.com>,
	"Mallick, Asit K" <asit.k.mallick@intel.com>,
	Jason Baron <jbaron@akamai.com>
Subject: Re: [PATCH 23/35] x86/speculation: Add basic speculation control code
Date: Fri, 19 Jan 2018 16:47:42 +0100	[thread overview]
Message-ID: <20180119154742.GA24935@redhat.com> (raw)
In-Reply-To: <0575AF4FD06DD142AD198903C74E1CC87A5E9136@ORSMSX103.amr.corp.intel.com>

On Fri, Jan 19, 2018 at 04:15:33AM +0000, Van De Ven, Arjan wrote:
> there is no such guarantee. Some of the IBRS implementations will
> actually flush rather than disable, or flush parts and disable other
> parts.

To me it helps in order to memorize the spec to understand why the
spec is the way it is.

I tried to help explaining some of that, but I notice that I created
more confusion... I never intended IBPB can be skipped in user to user
switches if leaving IBRS set in userland, that's not what we do and it
wouldn't be ok with certain smarter CPUs.

> yes the wording is a bit cryptic, but it's also very explicit about
> what it covers (and the rest is not covered!) and had to allow a few
> different implementations unfortunately.

We already follow the spec to the letter and we only depend on what is
covered there.

Surely the specs already explain everything better than I could ever
do, so if anything wasn't clear in the two previous emails where I
failed to explain the difference between setting or leaving IBRS set
in userland (ibrs_user) and setting or leaving STIBP set in userland
(stibp_user) you'll find all answers in the very explicit spec per
above quote.

Thanks,
Andrea

  reply	other threads:[~2018-01-19 15:47 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-01-18 13:48 [PATCH 00/35] jump_label, objtool, IBRS and IBPB Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 01/35] jump_label: Add branch hints to static_branch_{un,}likely() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 02/35] sched: Optimize ttwu_stat() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 03/35] x86: Reindent _static_cpu_has Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 04/35] x86: Update _static_cpu_has to use all named variables Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 05/35] x86: Add a type field to alt_instr Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 06/35] objtool: Implement base jump_assert support Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 07/35] x86: Annotate static_cpu_has alternative Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 08/35] objtool: Implement jump_assert for _static_cpu_has() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 09/35] objtool: Introduce special_type Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 10/35] x86/jump_label: Implement arch_static_assert() Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 11/35] objtool: Add retpoline validation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 12/35] x86/paravirt: Annotate indirect calls Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 13/35] x86,nospec: Annotate indirect calls/jumps Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 14/35] x86: Annotate indirect jump in head_64.S Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 15/35] objtool: More complex static jump implementation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 16/35] objtool: Use existing global variables for options Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 17/35] objtool: Even more complex static block checks Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 18/35] objtool: Another static block fail Peter Zijlstra, Peter Zijlstra
2018-01-19 16:42   ` Peter Zijlstra
2018-01-29 18:01     ` Josh Poimboeuf
2018-01-29 18:24       ` Peter Zijlstra
2018-01-18 13:48 ` [PATCH 19/35] objtool: Skip static assert when KCOV/KASAN Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 20/35] x86: Force asm-goto Peter Zijlstra, Peter Zijlstra
2018-01-18 16:25   ` David Woodhouse
2018-01-18 13:48 ` [PATCH 21/35] x86: Remove FAST_FEATURE_TESTS Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 22/35] x86/cpufeatures: Detect Speculation control feature Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 23/35] x86/speculation: Add basic speculation control code Peter Zijlstra, Peter Zijlstra
2018-01-18 16:37   ` Josh Poimboeuf
2018-01-18 17:08     ` Dave Hansen
2018-01-18 17:12       ` Paolo Bonzini
2018-01-18 18:24         ` Josh Poimboeuf
2018-01-18 19:08           ` Andrea Arcangeli
2018-01-18 23:25             ` Andy Lutomirski
2018-01-18 23:35               ` Andrew Cooper
2018-01-19  1:41               ` Andrea Arcangeli
2018-01-19  4:10                 ` Andy Lutomirski
2018-01-19  4:15                   ` Van De Ven, Arjan
2018-01-19 15:47                     ` Andrea Arcangeli [this message]
2018-01-18 13:48 ` [PATCH 24/35] x86/msr: Move native_*msr macros out of microcode.h Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 25/35] x86/speculation: Add inlines to control Indirect Branch Speculation Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 26/35] x86/enter: Create macros to stop/restart " Peter Zijlstra, Peter Zijlstra
2018-01-18 19:44   ` Tim Chen
2018-01-18 13:48 ` [PATCH 27/35] x86/enter: Use IBRS on syscall and interrupts Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 28/35] x86/idle: Control Indirect Branch Speculation in idle Peter Zijlstra, Peter Zijlstra
2018-01-18 19:52   ` Andrew Cooper
2018-01-18 13:48 ` [PATCH 29/35] x86/speculation: Add IPBP support Peter Zijlstra, Peter Zijlstra
2018-01-18 16:22   ` Josh Poimboeuf
2018-01-18 18:31   ` Borislav Petkov
2018-01-18 18:35     ` Josh Poimboeuf
2018-01-18 18:46       ` Borislav Petkov
2018-01-18 13:48 ` [PATCH 30/35] x86/speculation: Use Indirect Branch Prediction Barrier in context switch Peter Zijlstra, Peter Zijlstra
2018-01-19  0:38   ` Tim Chen
2018-01-19  4:03     ` Kevin Easton
2018-01-19 20:26       ` Tim Chen
2018-01-18 13:48 ` [PATCH 31/35] x86/ibrs: Add new helper macros to save/restore MSR_IA32_SPEC_CTRL Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 32/35] x86/vmx: Direct access to MSR_IA32_SPEC_CTRL Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 33/35] x86/svm: " Peter Zijlstra, Peter Zijlstra
2018-01-18 13:48 ` [PATCH 34/35] x86/kvm: Add IBPB support Peter Zijlstra, Peter Zijlstra
2018-01-18 15:32   ` Paolo Bonzini
2018-01-19 15:25     ` Paolo Bonzini
2018-01-19 16:08       ` David Woodhouse
2018-01-19 16:27         ` Andy Lutomirski
2018-01-19 16:48         ` Paolo Bonzini
2018-01-18 13:48 ` [PATCH 35/35] x86/nospec: Add static assertions Peter Zijlstra, Peter Zijlstra

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20180119154742.GA24935@redhat.com \
    --to=aarcange@redhat.com \
    --cc=ak@linux.intel.com \
    --cc=arjan.van.de.ven@intel.com \
    --cc=ashok.raj@intel.com \
    --cc=asit.k.mallick@intel.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@intel.com \
    --cc=dwmw2@infradead.org \
    --cc=gregkh@linuxfoundation.org \
    --cc=jbaron@akamai.com \
    --cc=jpoimboe@redhat.com \
    --cc=jun.nakajima@intel.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=luto@kernel.org \
    --cc=pbonzini@redhat.com \
    --cc=peterz@infradead.org \
    --cc=tglx@linutronix.de \
    --cc=tim.c.chen@linux.intel.com \
    --cc=torvalds@linux-foundation.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body. 
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.