From: Nadav Amit <namit@vmware.com>
To: Ingo Molnar <mingo@redhat.com>, Andy Lutomirski <luto@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Edward Cree <ecree@solarflare.com>
Cc: "H . Peter Anvin" <hpa@zytor.com>,
Thomas Gleixner <tglx@linutronix.de>,
LKML <linux-kernel@vger.kernel.org>,
Nadav Amit <nadav.amit@gmail.com>, X86 ML <x86@kernel.org>,
Paolo Abeni <pabeni@redhat.com>, Borislav Petkov <bp@alien8.de>,
David Woodhouse <dwmw@amazon.co.uk>,
Nadav Amit <namit@vmware.com>
Subject: [RFC v2 0/6] x86: dynamic indirect branch promotion
Date: Sun, 30 Dec 2018 23:21:06 -0800 [thread overview]
Message-ID: <20181231072112.21051-1-namit@vmware.com> (raw)
This is a revised version of optpolines (formerly named retpolines) for
dynamic indirect branch promotion in order to reduce retpoline overheads
[1].
This version address some of the concerns that were raised before.
Accordingly, the code was slightly simplified and patching is now done
using the regular int3/breakpoint mechanism.
Outline optpolines for multiple targets was added. I do not think the
way I implemented it is the correct one. In my original (private)
version, if there are more targets than the outline block can hold, the
outline block is completely removed. However, I think this is
more-or-less how Josh wanted it to be.
The code modifications are now done using a gcc-plugin. This allows to
easily ignore code from init and other code sections. I think it should
also allow us to add opt-in/opt-out support for each branch, for example
by marking function pointers using address-space attributes.
All of these changes required some optimizations to go away to keep the
code simple. I have still did not run the benchmarks again.
So I might have not addressed all the open issues, but it is rather hard
to finish the implementation since some still open high-level decisions
affect the way in which optimizations should be done.
Specifically:
- Is it going to be the only indirect branch promotion mechanism? If so,
it probably should also provide interface similar to Josh's
"static-calls" with annotations.
- Should it also be used when retpolines are disabled (in the config)?
This does complicate the implementation a bit (RFC v1 supported it).
- Is it going to be opt-in or opt-out? If it is an opt-out mechanism,
memory and performance optimizations need to be more aggressive.
- Do we use periodic learning or not? Josh suggested to reconfigure the
branches whenever a new target is found. However, I do not know at
this time how to do learning efficiently, without making learning much
more expensive.
[1] https://lore.kernel.org/patchwork/cover/1001332/
Nadav Amit (6):
x86: introduce kernel restartable sequence
objtool: ignore instructions
x86: patch indirect branch promotion
x86: interface for accessing indirect branch locations
x86: learning and patching indirect branch targets
x86: outline optpoline
arch/x86/Kconfig | 4 +
arch/x86/entry/entry_64.S | 16 +-
arch/x86/include/asm/nospec-branch.h | 83 ++
arch/x86/include/asm/sections.h | 2 +
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/asm-offsets.c | 9 +
arch/x86/kernel/nospec-branch.c | 1293 ++++++++++++++++++
arch/x86/kernel/traps.c | 7 +
arch/x86/kernel/vmlinux.lds.S | 7 +
arch/x86/lib/retpoline.S | 83 ++
include/linux/cpuhotplug.h | 1 +
include/linux/module.h | 9 +
kernel/module.c | 8 +
scripts/Makefile.gcc-plugins | 3 +
scripts/gcc-plugins/x86_call_markup_plugin.c | 329 +++++
tools/objtool/check.c | 21 +-
16 files changed, 1872 insertions(+), 4 deletions(-)
create mode 100644 arch/x86/kernel/nospec-branch.c
create mode 100644 scripts/gcc-plugins/x86_call_markup_plugin.c
--
2.17.1
next reply other threads:[~2018-12-31 7:20 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-31 7:21 Nadav Amit [this message]
2018-12-31 7:21 ` [RFC v2 1/6] x86: introduce kernel restartable sequence Nadav Amit
2018-12-31 20:08 ` Andy Lutomirski
2018-12-31 21:12 ` Nadav Amit
2019-01-03 22:21 ` Andi Kleen
2019-01-03 22:29 ` Nadav Amit
2019-01-03 22:48 ` Andi Kleen
2019-01-03 22:52 ` Nadav Amit
2019-01-03 23:40 ` Andi Kleen
2019-01-03 23:56 ` Nadav Amit
2019-01-04 0:34 ` hpa
2018-12-31 7:21 ` [RFC v2 2/6] objtool: ignore instructions Nadav Amit
2018-12-31 7:21 ` [RFC v2 3/6] x86: patch indirect branch promotion Nadav Amit
2018-12-31 7:21 ` [RFC v2 4/6] x86: interface for accessing indirect branch locations Nadav Amit
2018-12-31 7:21 ` [RFC v2 5/6] x86: learning and patching indirect branch targets Nadav Amit
2018-12-31 20:05 ` Andy Lutomirski
2018-12-31 21:07 ` Nadav Amit
2018-12-31 7:21 ` [RFC v2 6/6] x86: outline optpoline Nadav Amit
2018-12-31 19:51 ` [RFC v2 0/6] x86: dynamic indirect branch promotion Andy Lutomirski
2018-12-31 19:53 ` Nadav Amit
2019-01-03 18:10 ` Josh Poimboeuf
2019-01-03 18:30 ` Nadav Amit
2019-01-03 20:31 ` Josh Poimboeuf
2019-01-03 22:18 ` Andi Kleen
2019-01-07 16:32 ` Peter Zijlstra
2019-01-08 7:47 ` Adrian Hunter
2019-01-08 9:25 ` Peter Zijlstra
2019-01-08 10:01 ` Adrian Hunter
2019-01-08 10:10 ` Peter Zijlstra
2019-01-08 17:27 ` Andi Kleen
2019-01-08 18:28 ` Nadav Amit
2019-01-08 19:01 ` Peter Zijlstra
2019-01-08 20:47 ` Nadav Amit
2019-01-08 20:53 ` Andi Kleen
2019-01-09 10:35 ` Peter Zijlstra
2019-08-29 8:23 ` Tracing text poke / kernel self-modifying code (Was: Re: [RFC v2 0/6] x86: dynamic indirect branch promotion) Adrian Hunter
2019-08-29 8:53 ` Peter Zijlstra
2019-08-29 9:40 ` Adrian Hunter
2019-08-29 11:46 ` Peter Zijlstra
2019-09-12 7:00 ` Adrian Hunter
2019-09-12 12:17 ` hpa
2019-01-08 18:57 ` [RFC v2 0/6] x86: dynamic indirect branch promotion Peter Zijlstra
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