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Date: Thu, 14 Jul 2022 19:54:45 +0800
From: Qi Zheng <zhengqi.arch@...edance.com>
To: Arnd Bergmann <arnd@...db.de>
Cc: Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v1 2/2] arm64: support HAVE_IRQ_EXIT_ON_IRQ_STACK
On 2022/7/14 19:37, Arnd Bergmann wrote:
> On Fri, Jul 8, 2022 at 11:49 AM Qi Zheng <zhengqi.arch@...edance.com> wrote:
>>
>> Since softirqs are handled on the per-CPU IRQ stack,
>> let's support HAVE_IRQ_EXIT_ON_IRQ_STACK which causes
>> the core code to invoke __do_softirq() directly without
>> going through do_softirq_own_stack().
>>
>> Signed-off-by: Qi Zheng <zhengqi.arch@...edance.com>
>
> Adding Mark Rutland to Cc, he's the one that worked on this area the most in the
> past and should probably review your patch. I still feel like there
> should be a way
> to improve readability of the IRQ entry path rather than just adding another
Got it. And looking forward to reviews and suggestions from Mark or
anyone else.
> level of indirection, but the ideas I had so far have not led to
> anything useful.
>
> Overall I suppose your version is an improvement over the extra double stack
> switch when entering softirq.
>
> Arnd
Thanks,
Qi
>
>> ---
>> arch/arm64/Kconfig | 1 +
>> arch/arm64/include/asm/exception.h | 4 +++-
>> arch/arm64/kernel/entry-common.c | 30 ++++++++++++++++++++----------
>> arch/arm64/kernel/entry.S | 6 ++++--
>> arch/arm64/kernel/irq.c | 5 +++--
>> 5 files changed, 31 insertions(+), 15 deletions(-)
>>
>> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
>> index be0a9f0052ee..d2cc7daecce3 100644
>> --- a/arch/arm64/Kconfig
>> +++ b/arch/arm64/Kconfig
>> @@ -231,6 +231,7 @@ config ARM64
>> select TRACE_IRQFLAGS_SUPPORT
>> select TRACE_IRQFLAGS_NMI_SUPPORT
>> select HAVE_SOFTIRQ_ON_OWN_STACK
>> + select HAVE_IRQ_EXIT_ON_IRQ_STACK
>> help
>> ARM 64-bit (AArch64) Linux support.
>>
>> diff --git a/arch/arm64/include/asm/exception.h b/arch/arm64/include/asm/exception.h
>> index d94aecff9690..8bff0aa7ab50 100644
>> --- a/arch/arm64/include/asm/exception.h
>> +++ b/arch/arm64/include/asm/exception.h
>> @@ -54,7 +54,9 @@ asmlinkage void el0t_32_fiq_handler(struct pt_regs *regs);
>> asmlinkage void el0t_32_error_handler(struct pt_regs *regs);
>>
>> asmlinkage void call_on_irq_stack(struct pt_regs *regs,
>> - void (*func)(struct pt_regs *));
>> + void (*func)(struct pt_regs *),
>> + void (*do_func)(struct pt_regs *,
>> + void (*)(struct pt_regs *)));
>> asmlinkage void asm_exit_to_user_mode(struct pt_regs *regs);
>>
>> void do_mem_abort(unsigned long far, unsigned long esr, struct pt_regs *regs);
>> diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c
>> index c75ca36b4a49..935d1ab150b5 100644
>> --- a/arch/arm64/kernel/entry-common.c
>> +++ b/arch/arm64/kernel/entry-common.c
>> @@ -266,14 +266,16 @@ static void __sched arm64_preempt_schedule_irq(void)
>> }
>>
>> static void do_interrupt_handler(struct pt_regs *regs,
>> - void (*handler)(struct pt_regs *))
>> + void (*handler)(struct pt_regs *),
>> + void (*do_handler)(struct pt_regs *,
>> + void (*)(struct pt_regs *)))
>> {
>> struct pt_regs *old_regs = set_irq_regs(regs);
>>
>> if (on_thread_stack())
>> - call_on_irq_stack(regs, handler);
>> + call_on_irq_stack(regs, handler, do_handler);
>> else
>> - handler(regs);
>> + do_handler(regs, handler);
>>
>> set_irq_regs(old_regs);
>> }
>> @@ -441,22 +443,32 @@ asmlinkage void noinstr el1h_64_sync_handler(struct pt_regs *regs)
>> }
>> }
>>
>> +static void nmi_handler(struct pt_regs *regs, void (*handler)(struct pt_regs *))
>> +{
>> + handler(regs);
>> +}
>> +
>> static __always_inline void __el1_pnmi(struct pt_regs *regs,
>> void (*handler)(struct pt_regs *))
>> {
>> arm64_enter_nmi(regs);
>> - do_interrupt_handler(regs, handler);
>> + do_interrupt_handler(regs, handler, nmi_handler);
>> arm64_exit_nmi(regs);
>> }
>>
>> +static void irq_handler(struct pt_regs *regs, void (*handler)(struct pt_regs *))
>> +{
>> + irq_enter_rcu();
>> + handler(regs);
>> + irq_exit_rcu();
>> +}
>> +
>> static __always_inline void __el1_irq(struct pt_regs *regs,
>> void (*handler)(struct pt_regs *))
>> {
>> enter_from_kernel_mode(regs);
>>
>> - irq_enter_rcu();
>> - do_interrupt_handler(regs, handler);
>> - irq_exit_rcu();
>> + do_interrupt_handler(regs, handler, irq_handler);
>>
>> arm64_preempt_schedule_irq();
>>
>> @@ -699,9 +711,7 @@ static void noinstr el0_interrupt(struct pt_regs *regs,
>> if (regs->pc & BIT(55))
>> arm64_apply_bp_hardening();
>>
>> - irq_enter_rcu();
>> - do_interrupt_handler(regs, handler);
>> - irq_exit_rcu();
>> + do_interrupt_handler(regs, handler, irq_handler);
>>
>> exit_to_user_mode(regs);
>> }
>> diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
>> index 254fe31c03a0..1c351391f6bd 100644
>> --- a/arch/arm64/kernel/entry.S
>> +++ b/arch/arm64/kernel/entry.S
>> @@ -867,7 +867,9 @@ NOKPROBE(ret_from_fork)
>>
>> /*
>> * void call_on_irq_stack(struct pt_regs *regs,
>> - * void (*func)(struct pt_regs *));
>> + * void (*func)(struct pt_regs *)
>> + * void (*do_func)(struct pt_regs *,
>> + * void (*)(struct pt_regs *)));
>> *
>> * Calls func(regs) using this CPU's irq stack and shadow irq stack.
>> */
>> @@ -886,7 +888,7 @@ SYM_FUNC_START(call_on_irq_stack)
>>
>> /* Move to the new stack and call the function there */
>> mov sp, x16
>> - blr x1
>> + blr x2
>>
>> /*
>> * Restore the SP from the FP, and restore the FP and LR from the frame
>> diff --git a/arch/arm64/kernel/irq.c b/arch/arm64/kernel/irq.c
>> index c36ad20a52f3..003db605bc4f 100644
>> --- a/arch/arm64/kernel/irq.c
>> +++ b/arch/arm64/kernel/irq.c
>> @@ -73,14 +73,15 @@ static void init_irq_stacks(void)
>> #endif
>>
>> #ifndef CONFIG_PREEMPT_RT
>> -static void ____do_softirq(struct pt_regs *regs)
>> +static void ____do_softirq(struct pt_regs *regs,
>> + void (*handler)(struct pt_regs *))
>> {
>> __do_softirq();
>> }
>>
>> void do_softirq_own_stack(void)
>> {
>> - call_on_irq_stack(NULL, ____do_softirq);
>> + call_on_irq_stack(NULL, NULL, ____do_softirq);
>> }
>> #endif
>>
>> --
>> 2.20.1
>>
--
Thanks,
Qi
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