[PATCH v2 0/7] riscv: convert bottom half of exception handling to C

Jisheng Zhang
2024-07-20T17:26:49Z

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[1]
and my patches will touch the same exception asm code, so this series
is applied against Anton's patch.

patch1 and patch2 are cleanup patches.
patch3~patch7 do the conversion and some cleanup/optimization
after conversion.

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

However, there are two modifications I need to mention:

1. the cause I.E the CSR_CAUSE value is passed to do_traps() via. 2nd
param, do_traps() doesn't get it from pt_regs because this way an extra
memory load is needed, 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 conversion. Just
replace the excp_vect_table two entries.

Link: https://lore.kernel.org/linux-riscv/20240607061335.2197383-1-cyrilbur@tenstorrent.com/ [1]

since v1:
- add two clean up patches
- remove the two patches which fix imbalance in RAS, instead, explicitly
mark this series is applied against one of them.
- save cause in pt_regs prior to calling do_traps()
- do more clean up and optimization after the asm->c conversion:
staticalize and mark do_irq() as __always_inline.

Jisheng Zhang (7):
riscv: traps: staticalize handle_break()
riscv: traps: remove __visible annotation
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: staticalize and remove asmlinkage from updated functions
riscv: traps: mark do_irq() as __always_inline

arch/riscv/errata/sifive/errata.c | 25 +++++++---
arch/riscv/errata/sifive/errata_cip_453.S | 4 --
arch/riscv/include/asm/asm-prototypes.h | 20 +-------
arch/riscv/include/asm/entry-common.h | 1 -
arch/riscv/include/asm/errata_list.h | 21 ++-------
arch/riscv/kernel/entry.S | 57 +----------------------
arch/riscv/kernel/kernel_mode_vector.c | 2 +-
arch/riscv/kernel/traps.c | 55 ++++++++++++++++++----
8 files changed, 73 insertions(+), 112 deletions(-)

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2.43.0