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From: Peter Zijlstra <peterz@infradead.org>
To: x86@kernel.org, jpoimboe@redhat.com, andrew.cooper3@citrix.com
Cc: linux-kernel@vger.kernel.org, peterz@infradead.org,
	alexei.starovoitov@gmail.com, ndesaulniers@google.com
Subject: [PATCH v2 00/14] x86: Rewrite the retpoline rewrite logic
Date: Wed, 20 Oct 2021 12:44:42 +0200	[thread overview]
Message-ID: <20211020104442.021802560@infradead.org> (raw)

Hi,

These patches rewrite the way retpolines are rewritten. Currently objtool emits
alternative entries for most retpoline calls. However trying to extend that led
to trouble (ELF files are horrid).

Therefore completely overhaul this and have objtool emit a .retpoline_sites
section that lists all compiler generated retpoline thunk calls. Then the
kernel can do with them as it pleases.

Notably it will:

 - rewrite them to indirect instructions for !RETPOLINE
 - rewrite them to lfence; indirect; for RETPOLINE_AMD,
   where size allows (boo clang!)

Specifically, the !RETPOLINE case can now also deal with the clang-special
conditional-indirect-tail-call:

  Jcc __x86_indirect_thunk_\reg.

Finally, also update the x86 BPF jit to catch up to recent times and do these
same things.

All this should help improve performance by removing an indirection.

Patches can also be found here:

  git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git objtool/core


Changes since v1:
 - objtool: avoid self-modifying-code in .altinstr_replacement
 - objtool: shrink struct instruction
 - objtool: more cleanups
 - x86: more #ifdef
 - x86: GEN-for-each-reg cleanups/comments
 - x86: retpoline thunk array
 - x86,bpf: more complete retpoline replacement
 - build fixes

---
 arch/um/kernel/um_arch.c                |   4 +
 arch/x86/include/asm/GEN-for-each-reg.h |  13 ++-
 arch/x86/include/asm/alternative.h      |   1 +
 arch/x86/include/asm/asm-prototypes.h   |   6 +-
 arch/x86/include/asm/nospec-branch.h    |  59 ----------
 arch/x86/kernel/alternative.c           | 192 ++++++++++++++++++++++++++++++-
 arch/x86/kernel/cpu/bugs.c              |   7 --
 arch/x86/kernel/module.c                |   9 +-
 arch/x86/kernel/vmlinux.lds.S           |  14 +++
 arch/x86/lib/retpoline.S                |  50 ++------
 arch/x86/net/bpf_jit_comp.c             |  71 +++++++-----
 arch/x86/net/bpf_jit_comp32.c           |  22 +++-
 tools/objtool/arch/x86/decode.c         | 120 --------------------
 tools/objtool/check.c                   | 195 ++++++++++++++++++++++----------
 tools/objtool/elf.c                     |  84 --------------
 tools/objtool/include/objtool/check.h   |   1 -
 tools/objtool/include/objtool/elf.h     |   2 +-
 tools/objtool/special.c                 |   8 --
 18 files changed, 431 insertions(+), 427 deletions(-)


             reply	other threads:[~2021-10-20 11:01 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-20 10:44 Peter Zijlstra [this message]
2021-10-20 10:44 ` [PATCH v2 01/14] objtool: Tag retpoline thunk symbols Peter Zijlstra
2021-10-20 15:17   ` Josh Poimboeuf
2021-10-26  7:55     ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 02/14] objtool: Explicitly avoid self modifying code in .altinstr_replacement Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 03/14] objtool: Shrink struct instruction Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 04/14] objtool,x86: Replace alternatives with .retpoline_sites Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 05/14] x86/retpoline: Remove unused replacement symbols Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 06/14] x86/asm: Fix register order Peter Zijlstra
2021-10-22 19:27   ` David Laight
2021-10-25 14:09   ` Borislav Petkov
2021-10-20 10:44 ` [PATCH v2 07/14] x86/asm: Fixup odd GEN-for-each-reg.h usage Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 08/14] x86/retpoline: Create a retpoline thunk array Peter Zijlstra
2021-10-20 15:57   ` Josh Poimboeuf
2021-10-20 16:46     ` Andrew Cooper
2021-10-20 17:09       ` Josh Poimboeuf
2021-10-20 19:22         ` Peter Zijlstra
2021-10-20 19:43           ` Josh Poimboeuf
2021-10-20 19:34       ` Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 09/14] x86/alternative: Implement .retpoline_sites support Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 10/14] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 11/14] x86/alternative: Try inline spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 12/14] x86/alternative: Add debug prints to apply_retpolines() Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 13/14] x86,bugs: Unconditionally allow spectre_v2=retpoline,amd Peter Zijlstra
2021-10-20 10:44 ` [PATCH v2 14/14] bpf,x86: Respect X86_FEATURE_RETPOLINE* Peter Zijlstra
2021-10-20 11:09   ` Peter Zijlstra
2021-10-20 16:56     ` Josh Poimboeuf
2021-10-20 19:23       ` Peter Zijlstra
2021-10-21  0:05     ` Alexei Starovoitov
2021-10-21  8:47       ` Peter Zijlstra
2021-10-21 18:03         ` Alexei Starovoitov
2021-10-21 22:37           ` Peter Zijlstra
2021-10-21 23:24             ` Alexei Starovoitov
2021-10-21 23:38               ` Josh Poimboeuf
2021-10-21 23:42                 ` Alexei Starovoitov
2021-10-22 11:31                   ` Peter Zijlstra
2021-10-22 15:22                     ` Alexei Starovoitov
2021-10-25 13:44                       ` Maciej Fijalkowski
2021-10-25 12:42                         ` Peter Zijlstra
2021-10-21 23:51         ` Zvi Effron
2021-10-22  8:33           ` Peter Zijlstra
2021-10-22 21:06             ` Zvi Effron
2021-10-21  0:07   ` Alexei Starovoitov
2021-10-21  0:18     ` Josh Poimboeuf
2021-10-21  8:53       ` Peter Zijlstra

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