Message-ID: <20240610204821.230388-1-torvalds@linux-foundation.org>
Date: Mon, 10 Jun 2024 13:48:14 -0700
From: Linus Torvalds <torvalds@...ux-foundation.org>
To: Peter Anvin <hpa@...or.com>,
	Ingo Molnar <mingo@...nel.org>,
	Borislav Petkov <bp@...en8.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	the arch/x86 maintainers <x86@...nel.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-arch <linux-arch@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: [PATCH 0/7] arm64 / x86-64: low-level code generation issues

So this is the result of me doing some profiling on my 128-core Altra
box.  I've sent out versions of this before, but they've all been fairly
ugly partial series.

This is the full cleaned-up series with patches split up to be logical,
and with fixes from some of the commentary from previous patches.

The first four patches are for the 'runtime constant' code, where I did
the initial implementation on x86-64 just because I was more comfy with
that, and the arm64 version of it came once I had the x86-64 side
working.

The horror that is __d_lookup_rcu() shows up a lot more on my Altra box
because of the relatively pitiful caches, but it's something that I've
wanted on x86-64 before.  The arm64 numbers just made me bite the
bullet on the whole runtime constant thing.

The last three patches are purely arm64-specific, and just fix up some
nasty code generation in the user access functions.  I just noticed that
I will need to implement 'user_access_save()' for KCSAN now that I do
the unsafe user access functions. 

Anyway, that 'user_access_save/restore()' issue only shows up with
KCSAN.  And it would be a no-op thanks to arm64 doing SMAP the right way
(pet peeve: arm64 did what I told the x86 designers to do originally,
but they claimed was too hard, so we ended up with that CLAC/STAC
instead)... 

Sadly that "no-op for KCSAN" would is except for the horrid
CONFIG_ARM64_SW_TTBR0_PAN case, which is why I'm not touching it.  I'm
hoping some hapless^Whelpful arm64 person is willing to tackle this (or
maybe make KCSAN and ARM64_SW_TTBR0_PAN incompatible in the Kconfig). 

Note: the final access_ok() change in 7/7 is a API relaxation and
cleanup, and as such much more worrisome than the other patches.  It's
_simpler_ than the other patches, but the others aren't intended to
really change behavior.  That one does. 

Linus Torvalds (7):
  vfs: dcache: move hashlen_hash() from callers into d_hash()
  add default dummy 'runtime constant' infrastructure
  x86: add 'runtime constant' support
  arm64: add 'runtime constant' support
  arm64: start using 'asm goto' for get_user() when available
  arm64: start using 'asm goto' for put_user() when available
  arm64: access_ok() optimization

 arch/arm64/include/asm/runtime-const.h |  75 ++++++++++
 arch/arm64/include/asm/uaccess.h       | 191 +++++++++++++++++--------
 arch/arm64/kernel/mte.c                |  12 +-
 arch/arm64/kernel/vmlinux.lds.S        |   3 +
 arch/x86/include/asm/runtime-const.h   |  61 ++++++++
 arch/x86/kernel/vmlinux.lds.S          |   3 +
 fs/dcache.c                            |  17 ++-
 include/asm-generic/Kbuild             |   1 +
 include/asm-generic/runtime-const.h    |  15 ++
 include/asm-generic/vmlinux.lds.h      |   8 ++
 10 files changed, 319 insertions(+), 67 deletions(-)
 create mode 100644 arch/arm64/include/asm/runtime-const.h
 create mode 100644 arch/x86/include/asm/runtime-const.h
 create mode 100644 include/asm-generic/runtime-const.h

-- 
2.45.1.209.gc6f12300df

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