On 22/08/2024 14:30, Jinjie Ruan wrote:

On 2024/8/20 19:43, Kevin Brodsky wrote:

quoted

On 29/06/2024 10:56, Jinjie Ruan wrote:

quoted

Currently, x86, Riscv, Loongarch use the generic entry. Convert arm64
to use the generic entry infrastructure from kernel/entry/*. The generic
entry makes maintainers' work easier and codes more elegant, which also
removed duplicate 150+ LOC. The changes are below:

 - Remove TIF_SYSCALL_* flag, _TIF_WORK_MASK, _TIF_SYSCALL_WORK

 - Remove syscall_trace_enter/exit() and use generic one.

 - Remove *enter_from/exit_to_kernel_mode(), and wrap with generic
   irqentry_enter/exit().

 - Remove *enter_from/exit_to_user_mode(), and wrap with generic
   irqentry_enter_from/exit_to_user_mode().

 - Remove arm64_enter/exit_nmi() and use generic irqentry_nmi_enter/exit().

 - Remove PREEMPT_DYNAMIC code, as generic entry will do it ok by
   implementing arch_irqentry_exit_need_resched().

This is looking good to me overall, moving to using the generic helpers
is a clear improvement. I've tried my best to check that the new

Thank you very much for the review, It does make the code more clear.

quoted

implementation is functionally equivalent to the old. Ignoring additions
in the generic code (such as additional instrumentation_{begin,end}()
pairs or assertions), this seems to be the case, with one exception. The
MTE operations are done in a slightly different order on entry:

* mte_disable_tco_entry() was called *after* the generic lockdep/CT
functions in __enter_from_user_mode(). It is now called before those
generic operations - arch_enter_from_user_mode() called at the beginning
of enter_from_user_mode().

The most special for arm64 are these MTE operations, the comment for
__enter_from_kernel_mode() and __enter_from_user_mode() said:

   " Handle IRQ/context state management when entering from user/kernel
mode. Before this function is called it is not safe to call regular
kernel code "

I guess it is the reason why mte_disable_tco_entry() was called *after*
the generic lockdep/CT functions, but the first version of commit
38ddf7dafaeaf ("arm64: mte: avoid clearing PSTATE.TCO on entry unless
necessary") call it in arch/arm64/kernel/entry.S, so I think the order
is not so important.

Good point, before that commit TCO was disabled before any generic
exception code was run so changing the ordering of
mte_disable_tco_entry() is unlikely to be a problem (the current
implementation doesn't do anything complex).

quoted

* Similarly mte_disable_tco_entry() and mte_check_tfsr_entry() was
called after the generic operations in enter_from_kernel_mode(), and
they are now called after - arch_enter_from_kernel_mode() called at the
beginning of irqentry_enter().

This can be adjusted to be consistent.

I wonder if moving mte_check_tfsr_entry() is as harmless as
mte_disable_tco_entry(), because the former can cause a stack dump. Is
that safe to do before the lockdep/RCU handling? I would guess so but
would be good for someone to confirm.

Kevin