linux-kernel - [PATCH 0/6] riscv: convert bottom half of exception handling to C

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Date: Mon, 17 Jun 2024 01:05:47 +0800
From: Jisheng Zhang <jszhang@...nel.org>
To: Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Samuel Holland <samuel.holland@...ive.com>
Cc: linux-riscv@...ts.infradead.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH 0/6] riscv: convert bottom half of exception handling to C

For readability, maintainability and future scalability, convert the
bottom half of the exception handling to C.

During the conversion, I found Anton fixed a performance issue
and my patches will touch the same exception asm code, so I include
Anton's patch for completeness. I also cooked a similar patch to avoid
corrupting the RAS in ret_from_fork() per the inspiration.

Mostly the assembly code is converted to C in a relatively
straightforward manner.

However, there are two modifications I need to mention:

1. the CSR_CAUSE reg reading and saving is moved to the C code
because we need the cause to dispatch the exception handling,
if we keep the cause reading and saving, we either pass it to
do_traps() via. 2nd param or get it from pt_regs which an extra
memory load is needed, I don't like any of the two solutions becase
the exception handling sits in hot code path, every instruction
matters.

2.To cope with SIFIVE_CIP_453 errata, it looks like we don't need
alternative mechanism any more after the asm->c convertion. Just
replace the excp_vect_table two entries.

Anton Blanchard (1):
  riscv: Improve exception and system call latency

Jisheng Zhang (5):
  riscv: avoid corrupting the RAS
  riscv: convert bottom half of exception handling to C
  riscv: errata: remove ALT_INSN_FAULT and ALT_PAGE_FAULT
  riscv: errata: sifive: remove NOMMU handling
  riscv: remove asmlinkage from updated functions

 arch/riscv/errata/sifive/errata.c         | 25 +++++++---
 arch/riscv/errata/sifive/errata_cip_453.S |  4 --
 arch/riscv/include/asm/asm-prototypes.h   |  7 +--
 arch/riscv/include/asm/errata_list.h      | 21 ++------
 arch/riscv/kernel/entry.S                 | 61 ++---------------------
 arch/riscv/kernel/stacktrace.c            |  4 +-
 arch/riscv/kernel/traps.c                 | 57 ++++++++++++++++++---
 7 files changed, 81 insertions(+), 98 deletions(-)

-- 
2.43.0