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Message-ID: <346ecf28-807f-4ae9-be5d-08ebd649d241@ghiti.fr>
Date: Mon, 10 Mar 2025 10:58:15 +0100
From: Alexandre Ghiti <alex@...ti.fr>
To: Charlie Jenkins <charlie@...osinc.com>,
Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
<palmer@...belt.com>, Huacai Chen <chenhuacai@...nel.org>,
WANG Xuerui <kernel@...0n.name>, Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>,
Alexandre Ghiti <alexghiti@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
loongarch@...ts.linux.dev
Subject: Re: [PATCH v5 4/4] entry: Inline syscall_exit_to_user_mode()
Hi Charlie,
On 06/03/2025 01:43, Charlie Jenkins wrote:
> Architectures using the generic entry code can be optimized by having
> syscall_exit_to_user_mode inlined.
>
> Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
> ---
> include/linux/entry-common.h | 43 ++++++++++++++++++++++++++++++++++++--
> kernel/entry/common.c | 49 +-------------------------------------------
> 2 files changed, 42 insertions(+), 50 deletions(-)
>
> diff --git a/include/linux/entry-common.h b/include/linux/entry-common.h
> index fc61d0205c97084acc89c8e45e088946f5e6d9b2..f94f3fdf15fc0091223cc9f7b823970302e67312 100644
> --- a/include/linux/entry-common.h
> +++ b/include/linux/entry-common.h
> @@ -14,6 +14,7 @@
> #include <linux/kmsan.h>
>
> #include <asm/entry-common.h>
> +#include <asm/syscall.h>
>
> /*
> * Define dummy _TIF work flags if not defined by the architecture or for
> @@ -366,6 +367,15 @@ static __always_inline void exit_to_user_mode(void)
> lockdep_hardirqs_on(CALLER_ADDR0);
> }
>
> +/**
> + * syscall_exit_work - Handle work before returning to user mode
> + * @regs: Pointer to current pt_regs
> + * @work: Current thread syscall work
> + *
> + * Do one-time syscall specific work.
> + */
> +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
> @@ -379,7 +389,30 @@ static __always_inline void exit_to_user_mode(void)
> * make the final state transitions. Interrupts must stay disabled between
> * return from this function and the invocation of exit_to_user_mode().
> */
> -void syscall_exit_to_user_mode_work(struct pt_regs *regs);
> +static __always_inline void syscall_exit_to_user_mode_work(struct pt_regs *regs)
> +{
> + unsigned long work = READ_ONCE(current_thread_info()->syscall_work);
> + unsigned long nr = syscall_get_nr(current, regs);
> +
> + CT_WARN_ON(ct_state() != CT_STATE_KERNEL);
> +
> + if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
> + if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr))
> + local_irq_enable();
> + }
> +
> + rseq_syscall(regs);
> +
> + /*
> + * Do one-time syscall specific work. If these work items are
> + * enabled, we want to run them exactly once per syscall exit with
> + * interrupts enabled.
> + */
> + if (unlikely(work & SYSCALL_WORK_EXIT))
> + syscall_exit_work(regs, work);
> + local_irq_disable_exit_to_user();
> + exit_to_user_mode_prepare(regs);
> +}
>
> /**
> * syscall_exit_to_user_mode - Handle work before returning to user mode
> @@ -410,7 +443,13 @@ void syscall_exit_to_user_mode_work(struct pt_regs *regs);
> * exit_to_user_mode(). This function is preferred unless there is a
> * compelling architectural reason to use the separate functions.
> */
> -void syscall_exit_to_user_mode(struct pt_regs *regs);
> +static __always_inline void syscall_exit_to_user_mode(struct pt_regs *regs)
> +{
> + instrumentation_begin();
> + syscall_exit_to_user_mode_work(regs);
> + instrumentation_end();
> + exit_to_user_mode();
> +}
>
> /**
> * irqentry_enter_from_user_mode - Establish state before invoking the irq handler
> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index e33691d5adf7aab4af54cf2bf8e5ef5bd6ad1424..f55e421fb196dd5f9d4e34dd85ae096c774cf879 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -146,7 +146,7 @@ static inline bool report_single_step(unsigned long work)
> return work & SYSCALL_WORK_SYSCALL_EXIT_TRAP;
> }
>
> -static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
> +void syscall_exit_work(struct pt_regs *regs, unsigned long work)
> {
> bool step;
>
> @@ -173,53 +173,6 @@ static void syscall_exit_work(struct pt_regs *regs, unsigned long work)
> ptrace_report_syscall_exit(regs, step);
> }
>
> -/*
> - * Syscall specific exit to user mode preparation. Runs with interrupts
> - * enabled.
> - */
> -static 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);
> -
> - CT_WARN_ON(ct_state() != CT_STATE_KERNEL);
> -
> - if (IS_ENABLED(CONFIG_PROVE_LOCKING)) {
> - if (WARN(irqs_disabled(), "syscall %lu left IRQs disabled", nr))
> - local_irq_enable();
> - }
> -
> - rseq_syscall(regs);
> -
> - /*
> - * Do one-time syscall specific work. If these work items are
> - * enabled, we want to run them exactly once per syscall exit with
> - * interrupts enabled.
> - */
> - if (unlikely(work & SYSCALL_WORK_EXIT))
> - syscall_exit_work(regs, work);
> -}
> -
> -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);
> -}
> -
> -void syscall_exit_to_user_mode_work(struct pt_regs *regs)
> -{
> - __syscall_exit_to_user_mode_work(regs);
> -}
> -
> -__visible noinstr void syscall_exit_to_user_mode(struct pt_regs *regs)
> -{
> - instrumentation_begin();
> - __syscall_exit_to_user_mode_work(regs);
> - instrumentation_end();
> - exit_to_user_mode();
> -}
> -
> noinstr void irqentry_enter_from_user_mode(struct pt_regs *regs)
> {
> enter_from_user_mode(regs);
>
Reviewed-by: Alexandre Ghiti <alexghiti@...osinc.com>
Thanks,
Alex
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