linux-kernel - [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu

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Message-ID: <20250409211127.3544993-1-mingo@kernel.org>
Date: Wed,  9 Apr 2025 23:11:19 +0200
From: Ingo Molnar <mingo@...nel.org>
To: linux-kernel@...r.kernel.org
Cc: Andy Lutomirski <luto@...capital.net>,
	Dave Hansen <dave@...1.net>,
	Brian Gerst <brgerst@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Borislav Petkov <bp@...en8.de>,
	"H . Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Chang S . Bae" <chang.seok.bae@...el.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: [PATCH -v5 0/8] sched: Make task_struct::thread constant size, x86/fpu: Remove thread::fpu

This series is one of the dependencies of the fast-headers work,
which aims to reduce header complexity by removing <asm/processor.h>
from the <linux/sched.h> dependency chain, which headers are headers
are fat enough already even if we do not combine them.

To achieve that decoupling, one of the key steps is to not embedd any
C types from <asm/processor.h> into task_struct.

The only architecture that relies on that in a serious fashion is x86,
via the 'struct thread::fpu' variable size structure. The series below
attempts to resolve it by using a calculated fpu context area address
value via the x86_task_fpu() helper. The allocation layout of
task_struct + fpu-save-area doesn't change.

The -v5 version is a refresh of the -v4 series to v6.15-rc1.

The Git tree of these commits can also be found at:

  git://git.kernel.org/pub/scm/linux/kernel/git/mingo/tip.git WIP.x86/fpu

Thanks,

	Ingo

===============>
Ingo Molnar (8):
  x86/fpu: Introduce the x86_task_fpu() helper method
  x86/fpu: Convert task_struct::thread.fpu accesses to use x86_task_fpu()
  x86/fpu: Make task_struct::thread constant size
  x86/fpu: Remove the thread::fpu pointer
  x86/fpu: Push 'fpu' pointer calculation into the fpu__drop() call
  x86/fpu: Make sure x86_task_fpu() doesn't get called for PF_KTHREAD|PF_USER_WORKER tasks during exit
  x86/fpu: Remove init_task FPU state dependencies, add debugging warning for PF_KTHREAD tasks
  x86/fpu: Use 'fpstate' variable names consistently

 arch/x86/include/asm/fpu/api.h   |  2 +-
 arch/x86/include/asm/fpu/sched.h |  4 +-
 arch/x86/include/asm/processor.h | 23 ++++++------
 arch/x86/kernel/fpu/context.h    |  4 +-
 arch/x86/kernel/fpu/core.c       | 80 +++++++++++++++++++++++-----------------
 arch/x86/kernel/fpu/init.c       | 21 ++++++-----
 arch/x86/kernel/fpu/regset.c     | 22 +++++------
 arch/x86/kernel/fpu/signal.c     | 18 ++++-----
 arch/x86/kernel/fpu/xstate.c     | 27 ++++++--------
 arch/x86/kernel/fpu/xstate.h     |  6 +--
 arch/x86/kernel/process.c        |  9 ++---
 arch/x86/kernel/signal.c         |  6 +--
 arch/x86/kernel/traps.c          |  2 +-
 arch/x86/math-emu/fpu_aux.c      |  2 +-
 arch/x86/math-emu/fpu_entry.c    |  4 +-
 arch/x86/math-emu/fpu_system.h   |  2 +-
 arch/x86/mm/extable.c            |  2 +-
 include/linux/sched.h            | 15 ++------
 18 files changed, 126 insertions(+), 123 deletions(-)

-- 
2.45.2