linux-kernel - Re: [PATCH v1 02/13] riscv: add ISA extension probing for Zv* extensions

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Message-ID: <b157edc4-a21f-40ac-8c9f-e989b34bb872@rivosinc.com>
Date:   Thu, 12 Oct 2023 15:17:14 +0200
From:   Clément Léger <cleger@...osinc.com>
To:     linux-riscv@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc:     Palmer Dabbelt <palmer@...osinc.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Albert Ou <aou@...s.berkeley.edu>,
        Jonathan Corbet <corbet@....net>,
        Andrew Jones <ajones@...tanamicro.com>,
        Evan Green <evan@...osinc.com>, Conor Dooley <conor@...nel.org>
Subject: Re: [PATCH v1 02/13] riscv: add ISA extension probing for Zv*
 extensions



On 11/10/2023 13:14, Clément Léger wrote:
> Add probing of some Zv* ISA extensions that are mentioned in "RISC-V
> Cryptography Extensions Volume II" [1]. These ISA extensions are the
> following:
> 
> - Zvbb: Vector Basic Bit-manipulation
> - Zvbc: Vector Carryless Multiplication
> - Zvkb: Vector Cryptography Bit-manipulation
> - Zvkg: Vector GCM/GMAC.
> - Zvkned: NIST Suite: Vector AES Block Cipher
> - Zvknh[ab]: NIST Suite: Vector SHA-2 Secure Hash
> - Zvksed: ShangMi Suite: SM4 Block Cipher
> - Zvksh: ShangMi Suite: SM3 Secure Hash
> - Zvkn: NIST Algorithm Suite
> - Zvknc: NIST Algorithm Suite with carryless multiply
> - Zvkng: NIST Algorithm Suite with GCM.
> - Zvks: ShangMi Algorithm Suite
> - Zvksc: ShangMi Algorithm Suite with carryless multiplication
> - Zvksg: ShangMi Algorithm Suite with GCM.
> - Zvkt: Vector Data-Independent Execution Latency.
> 
> [1] https://drive.google.com/file/d/1gb9OLH-DhbCgWp7VwpPOVrrY6f3oSJLL/view
> 
> Signed-off-by: Clément Léger <cleger@...osinc.com>
> ---
>  arch/riscv/include/asm/hwcap.h | 16 ++++++++++++++++
>  arch/riscv/kernel/cpufeature.c | 16 ++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
> index b7b58258f6c7..4e46981ac6c8 100644
> --- a/arch/riscv/include/asm/hwcap.h
> +++ b/arch/riscv/include/asm/hwcap.h
> @@ -58,6 +58,22 @@
>  #define RISCV_ISA_EXT_ZICSR		40
>  #define RISCV_ISA_EXT_ZIFENCEI		41
>  #define RISCV_ISA_EXT_ZIHPM		42
> +#define RISCV_ISA_EXT_ZVBB		43
> +#define RISCV_ISA_EXT_ZVBC		44
> +#define RISCV_ISA_EXT_ZVKB		45
> +#define RISCV_ISA_EXT_ZVKG		46
> +#define RISCV_ISA_EXT_ZVKN		47
> +#define RISCV_ISA_EXT_ZVKNC		48
> +#define RISCV_ISA_EXT_ZVKNED		49
> +#define RISCV_ISA_EXT_ZVKNG		50
> +#define RISCV_ISA_EXT_ZVKNHA		51
> +#define RISCV_ISA_EXT_ZVKNHB		52
> +#define RISCV_ISA_EXT_ZVKS		53
> +#define RISCV_ISA_EXT_ZVKSC		54
> +#define RISCV_ISA_EXT_ZVKSED		55
> +#define RISCV_ISA_EXT_ZVKSH		56
> +#define RISCV_ISA_EXT_ZVKSG		57

About Zvks/Zvkn, these extensions are actually shorthand for a few other
sub-extensions, it is still not clear if it should be parsed as is.
There are multiple solutions:

- Handle them as-is, simply enable the extension, if reported through
hwprobe, userspace will be responsible to detect the sub-extensions
(current approach)

- "Unfold" the extension in order to enable all the sub-extensions and
keep the main one (for instance for Zvkn, enable Zvkned, Zvknhb, Zvkb,
Zvkt, Zvkn)

- "Unfold" but don't keep the extension "shorthand" in the ISA extension
list (for instance for Zvkn, enable Zvkned, Zvknhb, Zvkb, Zvkt)

Thanks,

Clément

> +#define RISCV_ISA_EXT_ZVKT		58
>  
>  #define RISCV_ISA_EXT_MAX		64
>  
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 1cfbba65d11a..859d647f3ced 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -174,6 +174,22 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(zba, RISCV_ISA_EXT_ZBA),
>  	__RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
>  	__RISCV_ISA_EXT_DATA(zbs, RISCV_ISA_EXT_ZBS),
> +	__RISCV_ISA_EXT_DATA(zvbb, RISCV_ISA_EXT_ZVBB),
> +	__RISCV_ISA_EXT_DATA(zvbc, RISCV_ISA_EXT_ZVBC),
> +	__RISCV_ISA_EXT_DATA(zvkb, RISCV_ISA_EXT_ZVKB),
> +	__RISCV_ISA_EXT_DATA(zvkg, RISCV_ISA_EXT_ZVKG),
> +	__RISCV_ISA_EXT_DATA(zvkn, RISCV_ISA_EXT_ZVKN),
> +	__RISCV_ISA_EXT_DATA(zvknc, RISCV_ISA_EXT_ZVKNC),
> +	__RISCV_ISA_EXT_DATA(zvkned, RISCV_ISA_EXT_ZVKNED),
> +	__RISCV_ISA_EXT_DATA(zvkng, RISCV_ISA_EXT_ZVKNG),
> +	__RISCV_ISA_EXT_DATA(zvknha, RISCV_ISA_EXT_ZVKNHA),
> +	__RISCV_ISA_EXT_DATA(zvknhb, RISCV_ISA_EXT_ZVKNHB),
> +	__RISCV_ISA_EXT_DATA(zvks, RISCV_ISA_EXT_ZVKS),
> +	__RISCV_ISA_EXT_DATA(zvksc, RISCV_ISA_EXT_ZVKSC),
> +	__RISCV_ISA_EXT_DATA(zvksed, RISCV_ISA_EXT_ZVKSED),
> +	__RISCV_ISA_EXT_DATA(zvksh, RISCV_ISA_EXT_ZVKSH),
> +	__RISCV_ISA_EXT_DATA(zvksg, RISCV_ISA_EXT_ZVKSG),
> +	__RISCV_ISA_EXT_DATA(zvkt, RISCV_ISA_EXT_ZVKT),
>  	__RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
>  	__RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
>  	__RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),