linux-kernel - [PATCH v1 0/3] x86: Allow variable-sized event frame

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Date: Mon, 17 Jun 2024 01:45:12 -0700
From: "Xin Li (Intel)" <xin@...or.com>
To: linux-kernel@...r.kernel.org
Cc: luto@...nel.org, tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        peterz@...radead.org, brgerst@...il.com
Subject: [PATCH v1 0/3] x86: Allow variable-sized event frame

This was initially posted as part of the FRED patch series and turned
down due to its unacceptable quality:
  https://lore.kernel.org/lkml/20230410081438.1750-31-xin3.li@intel.com/

And this is another attempt to meet the bar.

a FRED event frame could contain different amount of information for
different event types, e.g., #MCE could push extra bytes of information,
or perhaps even for different instances of the same event type. Thus
the size of an event frame pushed by a FRED CPU is not fixed and the
address of a pt_regs structure that is used to save the user level
context of current task is not at a fixed offset from top of current
task kernel stack.

This patch set adds a new field named 'user_pt_regs' in the thread_info
structure to save the address of user level context pt_regs structure,
thus to eliminate the need of any advance information of event frame
size and allow a FRED CPU to push variable-sized event frame.

With the above change, we can
1) Remove the padding space at top of the init stack because there is
   no user level context for init task.
2) Get rid of TOP_OF_KERNEL_STACK_PADDING on x86_64, which was defined
   to 0 for IDT to keep the code consistent with 32bit.

Xin Li (Intel) (3):
  x86/fred: Allow variable-sized event frame
  x86: Remove the padding space at top of the init stack
  x86: Get rid of TOP_OF_KERNEL_STACK_PADDING on x86_64

 arch/x86/entry/entry_fred.c        | 22 +++++++++++++++++
 arch/x86/include/asm/processor.h   | 38 +++++++++++++++++++++++-------
 arch/x86/include/asm/switch_to.h   |  2 +-
 arch/x86/include/asm/thread_info.h | 19 +++++----------
 arch/x86/kernel/process.c          | 21 +++++++++++++++++
 arch/x86/kernel/vmlinux.lds.S      | 18 ++++++++++++--
 include/linux/thread_info.h        |  1 +
 kernel/fork.c                      |  6 +++++
 8 files changed, 102 insertions(+), 25 deletions(-)

base-commit: 49b33979e3bf0a5424420d14f026de12f34e8b1e
-- 
2.45.1