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

[Clément Léger]

On 12/10/2023 16:10, Conor Dooley wrote:
> On Thu, Oct 12, 2023 at 03:17:14PM +0200, Clément Léger wrote:
>>
>>
>> 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@xxxxxxxxxxxx>
>>> ---
>>>  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)
> 
> I dislike this, since in-kernel users will have to check for "parent" &
> "child" extensions.
> 
>> - "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)
> 
> We threw together some code for this a few months ago after some
> discussion with some of your Rivos colleagues. The initial version of it
> was in this thread with Evan:
> https://lore.kernel.org/all/20230703-mangle-panning-75909ebbe30c@spud/
> and in a later iteration there was some more done by myself and Drew:
> https://lore.kernel.org/all/20230713-bootleg-tray-c5bfe58b5673@wendy/
> One of the versions ended up as the riscv-extensions-strings-scalar-crypto
> branch in my k.org repo:
> https://git.kernel.org/pub/scm/linux/kernel/git/conor/linux.git/log/?h=riscv-extensions-strings-scalar-crypto
> 

Thanks for these information ! I think your version to handle extension
group is pretty clean. Are you waiting for anything in particular except
a Signed-off: from Evan to submit that patch ? If so, can I backport
this patch in my branch, gather Evan SoB and rebase my series on top of it ?

> That crypto stuff has all gone quiet of late unfortunately. I wonder if
> Samuel is still working on it.

I talked with Samuel and we agreed on the following plan: I'll actually
carry on the bitmanip ISA part and he will resubmit the Zkr with
archrandom part.

> 
>> - "Unfold" but don't keep the extension "shorthand" in the ISA extension
>> list (for instance for Zvkn, enable Zvkned, Zvknhb, Zvkb, Zvkt)
> 
> But I would also be fine with this one from a pure in-kernel PoV.

Which is the case with your version FWIU (ie, only the child extensions
are visible).

> I think it's likely to be annoying for users though, since they won't be
> able to poll for the "parent" unless we re-assemble the parents in
> hwprobe etc (eugh).

Indeed, and re-assembling the parent is IMHO duplication of the existing
information. Checking that the needed ISA extensions are present will be
simple enough (simple bitmask) so I'm not sure that re-assembling the
parents is necessary (But that's a personal statement and I'm pretty
sure others will like it to be provided directly).

Thanks,

Clément

> 
> - don't permit passing the "parents" at all, and only deal with the
>   "children". We can enforce this for DT, but not for ACPI, so probably
>   not a runner>
> Thanks,
> Conor.
> 
>>
>> 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),