Re: [RFC PATCH v4 1/5] RISC-V: Detect and Enable Svadu Extension Support

[Andrew Jones]

On Fri, May 24, 2024 at 06:33:01PM GMT, Yong-Xuan Wang wrote:
> Svadu is a RISC-V extension for hardware updating of PTE A/D bits.
> 
> In this patch we detect Svadu extension support from DTB and enable it
> with SBI FWFT extension. Also we add arch_has_hw_pte_young() to enable
> optimization in MGLRU and __wp_page_copy_user() if Svadu extension is
> available.
> 
> Co-developed-by: Jinyu Tang <tjytimi@xxxxxxx>
> Signed-off-by: Jinyu Tang <tjytimi@xxxxxxx>
> Signed-off-by: Yong-Xuan Wang <yongxuan.wang@xxxxxxxxxx>
> Reviewed-by: Conor Dooley <conor.dooley@xxxxxxxxxxxxx>
> Reviewed-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>

I think this patch changed too much to keep r-b's. We didn't have the
FWFT part before.

> ---
>  arch/riscv/Kconfig               |  1 +
>  arch/riscv/include/asm/csr.h     |  1 +
>  arch/riscv/include/asm/hwcap.h   |  1 +
>  arch/riscv/include/asm/pgtable.h |  8 +++++++-
>  arch/riscv/kernel/cpufeature.c   | 11 +++++++++++
>  5 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index be09c8836d56..30fa558ee284 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -34,6 +34,7 @@ config RISCV
>  	select ARCH_HAS_PMEM_API
>  	select ARCH_HAS_PREPARE_SYNC_CORE_CMD
>  	select ARCH_HAS_PTE_SPECIAL
> +	select ARCH_HAS_HW_PTE_YOUNG
>  	select ARCH_HAS_SET_DIRECT_MAP if MMU
>  	select ARCH_HAS_SET_MEMORY if MMU
>  	select ARCH_HAS_STRICT_KERNEL_RWX if MMU && !XIP_KERNEL
> diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
> index 2468c55933cd..2ac270ad4acd 100644
> --- a/arch/riscv/include/asm/csr.h
> +++ b/arch/riscv/include/asm/csr.h
> @@ -194,6 +194,7 @@
>  /* xENVCFG flags */
>  #define ENVCFG_STCE			(_AC(1, ULL) << 63)
>  #define ENVCFG_PBMTE			(_AC(1, ULL) << 62)
> +#define ENVCFG_ADUE			(_AC(1, ULL) << 61)
>  #define ENVCFG_CBZE			(_AC(1, UL) << 7)
>  #define ENVCFG_CBCFE			(_AC(1, UL) << 6)
>  #define ENVCFG_CBIE_SHIFT		4
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index e17d0078a651..8d539e3f4e11 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -81,6 +81,7 @@
>  #define RISCV_ISA_EXT_ZTSO		72
>  #define RISCV_ISA_EXT_ZACAS		73
>  #define RISCV_ISA_EXT_XANDESPMU		74
> +#define RISCV_ISA_EXT_SVADU		75
>  
>  #define RISCV_ISA_EXT_XLINUXENVCFG	127
>  
> diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
> index 9f8ea0e33eb1..1f1b326ccf63 100644
> --- a/arch/riscv/include/asm/pgtable.h
> +++ b/arch/riscv/include/asm/pgtable.h
> @@ -117,6 +117,7 @@
>  #include <asm/tlbflush.h>
>  #include <linux/mm_types.h>
>  #include <asm/compat.h>
> +#include <asm/cpufeature.h>
>  
>  #define __page_val_to_pfn(_val)  (((_val) & _PAGE_PFN_MASK) >> _PAGE_PFN_SHIFT)
>  
> @@ -285,7 +286,6 @@ static inline pte_t pud_pte(pud_t pud)
>  }
>  
>  #ifdef CONFIG_RISCV_ISA_SVNAPOT
> -#include <asm/cpufeature.h>
>  
>  static __always_inline bool has_svnapot(void)
>  {
> @@ -621,6 +621,12 @@ static inline pgprot_t pgprot_writecombine(pgprot_t _prot)
>  	return __pgprot(prot);
>  }
>  
> +#define arch_has_hw_pte_young arch_has_hw_pte_young
> +static inline bool arch_has_hw_pte_young(void)
> +{
> +	return riscv_has_extension_unlikely(RISCV_ISA_EXT_SVADU);
> +}
> +
>  /*
>   * THP functions
>   */
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 3ed2359eae35..b023908c5932 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -93,6 +93,16 @@ static bool riscv_isa_extension_check(int id)
>  			return false;
>  		}
>  		return true;
> +	case RISCV_ISA_EXT_SVADU:
> +		if (sbi_probe_extension(SBI_EXT_FWFT) > 0) {

I think we've decided the appropriate way to prove for SBI extensions is
to first ensure the SBI version and then do the probe, like we do for STA
in has_pv_steal_clock()

> +			struct sbiret ret;
> +
> +			ret = sbi_ecall(SBI_EXT_FWFT, SBI_EXT_FWFT_SET, SBI_FWFT_PTE_AD_HW_UPDATING,
> +					1, 0, 0, 0, 0);
> +
> +			return ret.error == SBI_SUCCESS;
> +		}
> +		return false;
>  	case RISCV_ISA_EXT_INVALID:
>  		return false;
>  	}
> @@ -301,6 +311,7 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
>  	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
>  	__RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
> +	__RISCV_ISA_EXT_SUPERSET(svadu, RISCV_ISA_EXT_SVADU, riscv_xlinuxenvcfg_exts),

We do we need XLINUXENVCFG?

Thanks,
drew

>  	__RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
>  	__RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
>  	__RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
> -- 
> 2.17.1
>