Re: [PATCH v10 11/16] entry: Split syscall_exit_to_user_mode_work() for arch reuse

[Jinjie Ruan <ruanjinjie@huawei.com>]

On 2025/12/30 2:03, Kevin Brodsky wrote:
> On 22/12/2025 12:47, Jinjie Ruan wrote:
>> In the generic entry code, the beginning of
>> syscall_exit_to_user_mode_work() can be reused on arm64 so it makes
>> sense to split it.
>>
>> In preparation for moving arm64 over to the generic entry
>> code, split out syscall_exit_to_user_mode_work_prepare() helper from
>> syscall_exit_to_user_mode_work().
>>
>> No functional changes.
>>
>> Reviewed-by: Kevin Brodsky <kevin.brodsky@arm.com>
>> Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
>> Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
>> ---
>>  include/linux/entry-common.h | 35 ++++++++++++++++++++++-------------
>>  1 file changed, 22 insertions(+), 13 deletions(-)
>>
>> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
>> index 87efb38b7081..0de0e60630e1 100644
>> --- a/include/linux/entry-common.h
>> +++ b/include/linux/entry-common.h
>> @@ -121,20 +121,11 @@ static __always_inline long syscall_enter_from_user_mode(struct pt_regs *regs, l
>>   */
>>  void syscall_exit_work(struct pt_regs *regs, unsigned long work);
>>  
>> -/**
>> - * syscall_exit_to_user_mode_work - Handle work before returning to user mode
>> - * @regs:	Pointer to currents pt_regs
>> - *
>> - * Same as step 1 and 2 of syscall_exit_to_user_mode() but without calling
>> - * exit_to_user_mode() to perform the final transition to user mode.
>> - *
>> - * Calling convention is the same as for syscall_exit_to_user_mode() and it
>> - * returns with all work handled and interrupts disabled. The caller must
>> - * invoke exit_to_user_mode() before actually switching to user mode to
>> - * make the final state transitions. Interrupts must stay disabled between
>> - * return from this function and the invocation of exit_to_user_mode().
>> +/*
>> + * Syscall specific exit to user mode preparation. Runs with interrupts
>> + * enabled.
>>   */
>> -static __always_inline void syscall_exit_to_user_mode_work(struct pt_regs *regs)
>> +static __always_inline void syscall_exit_to_user_mode_work_prepare(struct pt_regs *regs)
>>  {
>>  	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
>>  	unsigned long nr = syscall_get_nr(current, regs);
>> @@ -155,6 +146,24 @@ static __always_inline void syscall_exit_to_user_mode_work(struct pt_regs *regs)
>>  	 */
>>  	if (unlikely(work & SYSCALL_WORK_EXIT))
>>  		syscall_exit_work(regs, work);
>> +}
>> +
>> +/**
>> + * syscall_exit_to_user_mode_work - Handle work before returning to user mode
>> + * @regs:	Pointer to currents pt_regs
>> + *
>> + * Same as step 1 and 2 of syscall_exit_to_user_mode() but without calling
>> + * exit_to_user_mode() to perform the final transition to user mode.
>> + *
>> + * Calling convention is the same as for syscall_exit_to_user_mode() and it
>> + * returns with all work handled and interrupts disabled. The caller must
>> + * invoke exit_to_user_mode() before actually switching to user mode to
>> + * make the final state transitions. Interrupts must stay disabled between
>> + * return from this function and the invocation of exit_to_user_mode().
>> + */
>> +static __always_inline void syscall_exit_to_user_mode_work(struct pt_regs *regs)
>> +{
>> +	syscall_exit_to_user_mode_work_prepare(regs);
> 
> The naming is getting awfully confusing, with the separate introduction
> of syscall_exit_to_user_mode_prepare().
> 
> Having had a closer look, do we really need
> syscall_exit_to_user_mode_work() as it currently stands? Nothing calls
> it except the generic syscall_exit_to_user_mode(). Which makes me think:
> how about moving the two lines below into syscall_exit_to_user_mode()
> instead of creating a new helper? IOW:

It looks fine to me, this will make the change less. The comment also
need to be updated.

> 
> @@ -155,8 +155,6 @@ static __always_inline void
> syscall_exit_to_user_mode_work(struct pt_regs *regs)
>       */
>      if (unlikely(work & SYSCALL_WORK_EXIT))
>          syscall_exit_work(regs, work);
> -    local_irq_disable_exit_to_user();
> -    syscall_exit_to_user_mode_prepare(regs);
>  }
>  
>  /**
> @@ -192,6 +190,8 @@ static __always_inline void
> syscall_exit_to_user_mode(struct pt_regs *regs)
>  {
>      instrumentation_begin();
>      syscall_exit_to_user_mode_work(regs);
> +    local_irq_disable_exit_to_user();
> +    syscall_exit_to_user_mode_prepare(regs);
>      instrumentation_end();
>      exit_to_user_mode();
>  }
> 
> - Kevin
> 
>>  	local_irq_disable_exit_to_user();
>>  	syscall_exit_to_user_mode_prepare(regs);
>>  }
>