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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,
	bpf@vger.kernel.org
Subject: [PATCH v3 00/16] x86: Rewrite the retpoline rewrite logic
Date: Tue, 26 Oct 2021 14:01:32 +0200	[thread overview]
Message-ID: <20211026120132.613201817@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 (soon) be found here:

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

Changes since v2:

 - rewrite the __x86_indirect_thunk_array[] stuff again
 - rewrite the retpoline,amd rewrite logic, it now also supports
   rewriting the Jcc case, if the original instruction is long enough, but
   more importantly, it's simpler code.
 - bpf label simplification patch
 - random assorted cleanups
 - actually managed to get bpf selftests working

---
 arch/um/kernel/um_arch.c                |   4 +
 arch/x86/include/asm/GEN-for-each-reg.h |  14 ++-
 arch/x86/include/asm/alternative.h      |   1 +
 arch/x86/include/asm/asm-prototypes.h   |  18 ---
 arch/x86/include/asm/nospec-branch.h    |  72 ++---------
 arch/x86/kernel/alternative.c           | 189 ++++++++++++++++++++++++++++-
 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                |  56 ++-------
 arch/x86/net/bpf_jit_comp.c             | 160 +++++++++---------------
 arch/x86/net/bpf_jit_comp32.c           |  22 +++-
 tools/objtool/arch/x86/decode.c         | 120 ------------------
 tools/objtool/check.c                   | 208 ++++++++++++++++++++++----------
 tools/objtool/elf.c                     |  84 -------------
 tools/objtool/include/objtool/check.h   |   1 -
 tools/objtool/include/objtool/elf.h     |   6 +-
 tools/objtool/special.c                 |   8 --
 18 files changed, 472 insertions(+), 521 deletions(-)


             reply	other threads:[~2021-10-26 12:05 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-26 12:01 Peter Zijlstra [this message]
2021-10-26 12:01 ` [PATCH v3 01/16] objtool: Classify symbols Peter Zijlstra
2021-10-28  3:58   ` Josh Poimboeuf
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 02/16] objtool: Explicitly avoid self modifying code in .altinstr_replacement Peter Zijlstra
2021-10-28  4:01   ` Josh Poimboeuf
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 03/16] objtool: Shrink struct instruction Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 04/16] objtool,x86: Replace alternatives with .retpoline_sites Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 05/16] x86/retpoline: Remove unused replacement symbols Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 06/16] x86/asm: Fix register order Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 07/16] x86/asm: Fixup odd GEN-for-each-reg.h usage Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 08/16] x86/retpoline: Move the retpoline thunk declarations to nospec-branch.h Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 09/16] x86/retpoline: Create a retpoline thunk array Peter Zijlstra
2021-10-29  8:03   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 10/16] x86/alternative: Implement .retpoline_sites support Peter Zijlstra
2021-10-27 17:38   ` Borislav Petkov
2021-10-27 19:10     ` Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 11/16] x86/alternative: Handle Jcc __x86_indirect_thunk_\reg Peter Zijlstra
2021-10-28  9:29   ` Borislav Petkov
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 12/16] x86/alternative: Try inline spectre_v2=retpoline,amd Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 13/16] x86/alternative: Add debug prints to apply_retpolines() Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 14/16] x86,bugs: Unconditionally allow spectre_v2=retpoline,amd Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 15/16] bpf, x86: Simplify computing label offsets Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] bpf,x86: " tip-bot2 for Peter Zijlstra
2021-10-26 12:01 ` [PATCH v3 16/16] bpf,x86: Respect X86_FEATURE_RETPOLINE* Peter Zijlstra
2021-10-29  8:02   ` [tip: objtool/core] " tip-bot2 for Peter Zijlstra
2021-10-26 18:26 ` [PATCH v3 00/16] x86: Rewrite the retpoline rewrite logic Alexei Starovoitov
2021-10-26 18:45   ` Peter Zijlstra
2021-10-26 20:00     ` Alexei Starovoitov
2021-10-26 21:05       ` Peter Zijlstra
2021-10-26 21:05         ` Alexei Starovoitov
2021-10-27  9:00           ` Peter Zijlstra
2021-10-27 17:32             ` Alexei Starovoitov
2021-10-28  5:17 ` Josh Poimboeuf
2021-10-28 17:43 ` Borislav Petkov
2021-10-29 12:43 ` Miroslav Benes

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