Re: [PATCH v10 5/7] RISC-V: Allow marking IPIs as suitable for remote FENCEs

[Atish Patra]

On Tue, Nov 1, 2022 at 7:34 AM Anup Patel <apatel@xxxxxxxxxxxxxxxx> wrote:
>
> To do remote FENCEs (i.e. remote TLB flushes) using IPI calls on the
> RISC-V kernel, we need hardware mechanism to directly inject IPI from
> the supervisor mode (i.e. RISC-V kernel) instead of using SBI calls.
>
> The upcoming AIA IMSIC devices allow direct IPI injection from the
> supervisor mode (i.e. RISC-V kernel). To support this, we extend the
> riscv_ipi_set_virq_range() function so that IPI provider (i.e. irqchip
> drivers can mark IPIs as suitable for remote FENCEs.
>
> Signed-off-by: Anup Patel <apatel@xxxxxxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/smp.h      | 18 ++++++++++++++++--
>  arch/riscv/kernel/sbi-ipi.c       |  2 +-
>  arch/riscv/kernel/smp.c           | 11 ++++++++++-
>  drivers/clocksource/timer-clint.c |  2 +-
>  4 files changed, 28 insertions(+), 5 deletions(-)
>
> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> index 79ed0b73cd4e..56976e41a21e 100644
> --- a/arch/riscv/include/asm/smp.h
> +++ b/arch/riscv/include/asm/smp.h
> @@ -16,6 +16,9 @@ struct seq_file;
>  extern unsigned long boot_cpu_hartid;
>
>  #ifdef CONFIG_SMP
> +
> +#include <linux/jump_label.h>
> +
>  /*
>   * Mapping between linux logical cpu index and hartid.
>   */
> @@ -46,7 +49,12 @@ void riscv_ipi_disable(void);
>  bool riscv_ipi_have_virq_range(void);
>
>  /* Set the IPI interrupt numbers for arch (called by irqchip drivers) */
> -void riscv_ipi_set_virq_range(int virq, int nr);
> +void riscv_ipi_set_virq_range(int virq, int nr, bool use_for_rfence);
> +
> +/* Check if we can use IPIs for remote FENCEs */
> +DECLARE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
> +#define riscv_use_ipi_for_rfence() \
> +       static_branch_unlikely(&riscv_ipi_for_rfence)
>
>  /* Secondary hart entry */
>  asmlinkage void smp_callin(void);
> @@ -93,10 +101,16 @@ static inline bool riscv_ipi_have_virq_range(void)
>         return false;
>  }
>
> -static inline void riscv_ipi_set_virq_range(int virq, int nr)
> +static inline void riscv_ipi_set_virq_range(int virq, int nr,
> +                                           bool use_for_rfence)
>  {
>  }
>
> +static inline bool riscv_use_ipi_for_rfence(void)
> +{
> +       return false;
> +}
> +
>  #endif /* CONFIG_SMP */
>
>  #if defined(CONFIG_HOTPLUG_CPU) && (CONFIG_SMP)
> diff --git a/arch/riscv/kernel/sbi-ipi.c b/arch/riscv/kernel/sbi-ipi.c
> index f0a78420b127..ee8620104bd8 100644
> --- a/arch/riscv/kernel/sbi-ipi.c
> +++ b/arch/riscv/kernel/sbi-ipi.c
> @@ -75,6 +75,6 @@ void __init sbi_ipi_init(void)
>                           "irqchip/sbi-ipi:starting",
>                           sbi_ipi_starting_cpu, sbi_ipi_dying_cpu);
>
> -       riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
> +       riscv_ipi_set_virq_range(virq, BITS_PER_BYTE, false);
>         pr_info("providing IPIs using SBI IPI extension\n");
>  }
> diff --git a/arch/riscv/kernel/smp.c b/arch/riscv/kernel/smp.c
> index e8a20454d65b..74b8cb1a89ab 100644
> --- a/arch/riscv/kernel/smp.c
> +++ b/arch/riscv/kernel/smp.c
> @@ -145,7 +145,10 @@ bool riscv_ipi_have_virq_range(void)
>         return (ipi_virq_base) ? true : false;
>  }
>
> -void riscv_ipi_set_virq_range(int virq, int nr)
> +DEFINE_STATIC_KEY_FALSE(riscv_ipi_for_rfence);
> +EXPORT_SYMBOL_GPL(riscv_ipi_for_rfence);
> +
> +void riscv_ipi_set_virq_range(int virq, int nr, bool use_for_rfence)
>  {
>         int i, err;
>
> @@ -168,6 +171,12 @@ void riscv_ipi_set_virq_range(int virq, int nr)
>
>         /* Enabled IPIs for boot CPU immediately */
>         riscv_ipi_enable();
> +
> +       /* Update RFENCE static key */
> +       if (use_for_rfence)
> +               static_branch_enable(&riscv_ipi_for_rfence);
> +       else
> +               static_branch_disable(&riscv_ipi_for_rfence);
>  }
>  EXPORT_SYMBOL_GPL(riscv_ipi_set_virq_range);
>
> diff --git a/drivers/clocksource/timer-clint.c b/drivers/clocksource/timer-clint.c
> index f9dd746a72c5..658049a5440b 100644
> --- a/drivers/clocksource/timer-clint.c
> +++ b/drivers/clocksource/timer-clint.c
> @@ -249,7 +249,7 @@ static int __init clint_timer_init_dt(struct device_node *np)
>                 goto fail_free_irq;
>         }
>
> -       riscv_ipi_set_virq_range(virq, BITS_PER_BYTE);
> +       riscv_ipi_set_virq_range(virq, BITS_PER_BYTE, true);
>         clint_clear_ipi(clint_ipi_irq, NULL);
>
>         return 0;
> --
> 2.34.1
>


Reviewed-by: Atish Patra <atishp@xxxxxxxxxxxx>
-- 
Regards,
Atish