linux-kernel - Re: [PATCH v2 05/19] riscv: add ISA extension parsing for vector crypto extensions

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Message-ID: <c64d9ddb-edbd-4c8f-b56f-1b90d82100b7@rivosinc.com>
Date:   Mon, 23 Oct 2023 09:14:45 +0200
From:   Clément Léger <cleger@...osinc.com>
To:     7626f978-e9ea-4f8f-b814-aeac02bd3712@...osinc.com
Cc:     Evan Green <evan@...osinc.com>, linux-riscv@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, 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>,
        Conor Dooley <conor@...nel.org>,
        Samuel Ortiz <sameo@...osinc.com>
Subject: Re: [PATCH v2 05/19] riscv: add ISA extension parsing for vector
 crypto extensions



On 20/10/2023 04:43, Jerry Shih wrote:
> On Oct 19, 2023, at 17:35, Clément Léger <cleger@...osinc.com> wrote:
>> On 18/10/2023 19:26, Evan Green wrote:
>>> On Wed, Oct 18, 2023 at 5:53 AM Clément Léger <cleger@...osinc.com> wrote:
>>>>
>>>> On 18/10/2023 03:45, Jerry Shih wrote:
>>>>>
>>>>> The `Zvkb` is the subset of `Zvbb`[1]. So, the `Zvkb` should be bundled with `Zvbb`.
>>>>
>>>> Hi Jerry,
>>>>
>>>> Thanks for catching this, I think some other extensions will fall in
>>>> this category as well then (Zvknha/Zvknhb). I will verify that.
>>>
>>> The bundling mechanism works well when an extension is a pure lasso
>>> around other extensions. We'd have to tweak that code if we wanted to
>>> support cases like this, where the extension is a superset of others,
>>> but also contains loose change not present anywhere else (and
>>> therefore also needs to stand as a separate bit).
>>
>> For Zvbb and Zvknhb, I used the following code:
>>
>> static const unsigned int riscv_zvbb_bundled_exts[] = {
>> 	RISCV_ISA_EXT_ZVKB,
>> 	RISCV_ISA_EXT_ZVBB
>> };
>>
>> static const unsigned int riscv_zvknhb_bundled_exts[] = {
>> 	RISCV_ISA_EXT_ZVKNHA,
>> 	RISCV_ISA_EXT_ZVKNHB
>> };
>>
>> Which correctly results in both extension (superset + base set) being
>> enabled when only one is set. Is there something that I'm missing ?
> 
> We should not bundle zvknha and zvknhb together. They are exclusive.

Yes, but for instance, what happens if the user query the zvknha (if it
only needs SHA256) but zvknhb is present. If we don't declare zvknha,
then it will fail but the support would actually be present due to
zvknhb being there.

Clément


> Please check:
> https://github.com/riscv/riscv-crypto/issues/364#issuecomment-1726782096
> 
> -Jerry
>