Re: [PATCH v3 08/17] riscv: misaligned: add a function to check misalign trap delegability

Andrew Jones
2025-03-13T13:19:35Z

On Mon, Mar 10, 2025 at 04:12:15PM +0100, Clément Léger wrote:
> Checking for the delegability of the misaligned access trap is needed
> for the KVM FWFT extension implementation. Add a function to get the
> delegability of the misaligned trap exception.
>
> Signed-off-by: Clément Léger <cleger@rivosinc.com>
> ---
> arch/riscv/include/asm/cpufeature.h | 5 +++++
> arch/riscv/kernel/traps_misaligned.c | 17 +++++++++++++++--
> 2 files changed, 20 insertions(+), 2 deletions(-)
>
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index ad7d26788e6a..8b97cba99fc3 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -69,12 +69,17 @@ int cpu_online_unaligned_access_init(unsigned int cpu);
> #if defined(CONFIG_RISCV_SCALAR_MISALIGNED)
> void unaligned_emulation_finish(void);
> bool unaligned_ctl_available(void);
> +bool misaligned_traps_can_delegate(void);
> DECLARE_PER_CPU(long, misaligned_access_speed);
> #else
> static inline bool unaligned_ctl_available(void)
> {
> return false;
> }
> +static inline bool misaligned_traps_can_delegate(void)
> +{
> + return false;
> +}
> #endif
>
> bool check_vector_unaligned_access_emulated_all_cpus(void);
> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
> index db31966a834e..a67a6e709a06 100644
> --- a/arch/riscv/kernel/traps_misaligned.c
> +++ b/arch/riscv/kernel/traps_misaligned.c
> @@ -716,10 +716,10 @@ static int cpu_online_check_unaligned_access_emulated(unsigned int cpu)
> }
> #endif
>
> -#ifdef CONFIG_RISCV_SBI
> -
> static bool misaligned_traps_delegated;
>
> +#ifdef CONFIG_RISCV_SBI
> +
> static int cpu_online_sbi_unaligned_setup(unsigned int cpu)
> {
> if (sbi_fwft_set(SBI_FWFT_MISALIGNED_EXC_DELEG, 1, 0) &&
> @@ -761,6 +761,7 @@ static int cpu_online_sbi_unaligned_setup(unsigned int cpu __always_unused)
> {
> return 0;
> }
> +
> #endif
>
> int cpu_online_unaligned_access_init(unsigned int cpu)
> @@ -773,3 +774,15 @@ int cpu_online_unaligned_access_init(unsigned int cpu)
>
> return cpu_online_check_unaligned_access_emulated(cpu);
> }
> +
> +bool misaligned_traps_can_delegate(void)
> +{
> + /*
> + * Either we successfully requested misaligned traps delegation for all
> + * CPUS or the SBI does not implemented FWFT extension but delegated the
> + * exception by default.
> + */
> + return misaligned_traps_delegated ||
> + all_cpus_unaligned_scalar_access_emulated();
> +}
> +EXPORT_SYMBOL_GPL(misaligned_traps_can_delegate);
> \ No newline at end of file

Check your editor settings.

> --
> 2.47.2

Reviewed-by: Andrew Jones <ajones@ventanamicro.com>