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

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
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().

* 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().

I am not under the impression that these ordering changes are
problematic, but I may be missing something.

[...]
 
-/*
- * Handle IRQ/context state management when entering from kernel mode.
- * Before this function is called it is not safe to call regular kernel code,
- * instrumentable code, or any code which may trigger an exception.
- *
- * This is intended to match the logic in irqentry_enter(), handling the kernel
- * mode transitions only.
- */
-static __always_inline void __enter_from_kernel_mode(struct pt_regs *regs)
-{
-	regs->exit_rcu = false;

exit_rcu in struct pt_regs is unused now that these functions are gone
so it can be removed.

arm64_{enter,exit}_el1_dbg() have apparently no generic counterparts we
can replace them with, but maybe we could align them with the generic
functions some more? Specifically, I'm thinking about making them
return/take an irqentry_state_t just like irqentry_nmi_{enter,exit}().
This way we can get rid of struct pt_regs::lockdep_hardirqs, which is
now only used by those functions.

 		lockdep_hardirqs_on(CALLER_ADDR0);
 }
 
-#ifdef CONFIG_PREEMPT_DYNAMIC
-DEFINE_STATIC_KEY_TRUE(sk_dynamic_irqentry_exit_cond_resched);

The key is declared in asm/preempt.h, that declaration should also be
removed.

Kevin

[...]