linux-kernel - Re: [PATCH v7 04/11] entry: Add syscall_exit_to_user_mode

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Message-ID: <af048915-40d3-4007-880a-090c1f079e59@arm.com>
Date: Tue, 18 Nov 2025 18:11:13 +0100
From: Kevin Brodsky <kevin.brodsky@....com>
To: Jinjie Ruan <ruanjinjie@...wei.com>, catalin.marinas@....com,
 will@...nel.org, oleg@...hat.com, tglx@...utronix.de, peterz@...radead.org,
 luto@...nel.org, shuah@...nel.org, kees@...nel.org, wad@...omium.org,
 akpm@...ux-foundation.org, ldv@...ace.io, macro@...am.me.uk, deller@....de,
 mark.rutland@....com, song@...nel.org, mbenes@...e.cz, ryan.roberts@....com,
 ada.coupriediaz@....com, anshuman.khandual@....com, broonie@...nel.org,
 pengcan@...inos.cn, dvyukov@...gle.com, kmal@...k.li, lihongbo22@...wei.com,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v7 04/11] entry: Add syscall_exit_to_user_mode_prepare()
 helper

On 17/11/2025 14:30, Jinjie Ruan wrote:
> In the generic entry code, the part before
> syscall_exit_to_user_mode_work() calls syscall_exit_work(), which
> serves the same purpose as syscall_exit_to_user_mode_prepare()
> in arm64.

This is really hard to parse, I suppose the point is that the beginning
of syscall_exit_to_user_mode_work() can be reused on arm64 and therefore
it makes sense to split it?

> In preparation for moving arm64 over to the generic entry
> code, extract syscall_exit_to_user_mode_prepare() helper from
> syscall_exit_to_user_mode_work().
>
> No functional changes.
>
> Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>

The position of this patch in the series seems a little arbitrary (it
has no dependency on other patches), it might make more sense to group
it with the other generic patches (i.e. move it to patch 7).

Otherwise:

Reviewed-by: Kevin Brodsky <kevin.brodsky@....com>

- Kevin

> ---
>  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 7177436f0f9e..cd6dacb2d8bf 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -137,20 +137,11 @@ 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_prepare(struct pt_regs *regs)
>  {
>  	unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
>  	unsigned long nr = syscall_get_nr(current, regs);
> @@ -171,6 +162,24 @@ 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_prepare(regs);
>  	local_irq_disable_exit_to_user();
>  	exit_to_user_mode_prepare(regs);
>  }