Re: [PATCH -fixes v2 3/4] riscv: Add ISA extension parsing for Sm and Ss

[Samuel Holland]

On 2024-02-13 12:07 PM, Conor Dooley wrote:
> On Mon, Feb 12, 2024 at 07:37:34PM -0800, Samuel Holland wrote:
>> Previously, all extension version numbers were ignored. However, the
>> version number is important for these two extensions. The simplest way
>> to implement this is to use a separate bitmap bit for each supported
>> version, with each successive version implying all of the previous ones.
>> This allows alternatives and riscv_has_extension_[un]likely() to work
>> naturally.
>>
>> To avoid duplicate extensions in /proc/cpuinfo, the new successor_id
>> field allows hiding all but the newest implemented version of an
>> extension.
>>
>> Cc: <stable@xxxxxxxxxxxxxxx> # v6.7+
>> Signed-off-by: Samuel Holland <samuel.holland@xxxxxxxxxx>
>> ---
>>
>> Changes in v2:
>>  - New patch for v2
>>
>>  arch/riscv/include/asm/cpufeature.h |  1 +
>>  arch/riscv/include/asm/hwcap.h      |  8 ++++++
>>  arch/riscv/kernel/cpu.c             |  5 ++++
>>  arch/riscv/kernel/cpufeature.c      | 42 +++++++++++++++++++++++++----
>>  4 files changed, 51 insertions(+), 5 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
>> index 0bd11862b760..ac71384e7bc4 100644
>> --- a/arch/riscv/include/asm/cpufeature.h
>> +++ b/arch/riscv/include/asm/cpufeature.h
>> @@ -61,6 +61,7 @@ struct riscv_isa_ext_data {
>>  	const char *property;
>>  	const unsigned int *subset_ext_ids;
>>  	const unsigned int subset_ext_size;
>> +	const unsigned int successor_id;
>>  };
>>  
>>  extern const struct riscv_isa_ext_data riscv_isa_ext[];
>> diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
>> index 5340f818746b..5b51aa1db15b 100644
>> --- a/arch/riscv/include/asm/hwcap.h
>> +++ b/arch/riscv/include/asm/hwcap.h
>> @@ -80,13 +80,21 @@
>>  #define RISCV_ISA_EXT_ZFA		71
>>  #define RISCV_ISA_EXT_ZTSO		72
>>  #define RISCV_ISA_EXT_ZACAS		73
>> +#define RISCV_ISA_EXT_SM1p11		74
>> +#define RISCV_ISA_EXT_SM1p12		75
>> +#define RISCV_ISA_EXT_SS1p11		76
>> +#define RISCV_ISA_EXT_SS1p12		77
>>  
>>  #define RISCV_ISA_EXT_MAX		128
>>  #define RISCV_ISA_EXT_INVALID		U32_MAX
>>  
>>  #ifdef CONFIG_RISCV_M_MODE
>> +#define RISCV_ISA_EXT_Sx1p11		RISCV_ISA_EXT_SM1p11
>> +#define RISCV_ISA_EXT_Sx1p12		RISCV_ISA_EXT_SM1p12
>>  #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SMAIA
>>  #else
>> +#define RISCV_ISA_EXT_Sx1p11		RISCV_ISA_EXT_SS1p11
>> +#define RISCV_ISA_EXT_Sx1p12		RISCV_ISA_EXT_SS1p12
>>  #define RISCV_ISA_EXT_SxAIA		RISCV_ISA_EXT_SSAIA
>>  #endif
>>  
>> diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
>> index d11d6320fb0d..2e6b90ed0d51 100644
>> --- a/arch/riscv/kernel/cpu.c
>> +++ b/arch/riscv/kernel/cpu.c
>> @@ -215,6 +215,11 @@ static void print_isa(struct seq_file *f, const unsigned long *isa_bitmap)
>>  		if (!__riscv_isa_extension_available(isa_bitmap, riscv_isa_ext[i].id))
>>  			continue;
>>  
>> +		/* Only show the newest implemented version of an extension */
>> +		if (riscv_isa_ext[i].successor_id != RISCV_ISA_EXT_INVALID &&
>> +		    __riscv_isa_extension_available(isa_bitmap, riscv_isa_ext[i].successor_id))
>> +			continue;
>> +
>>  		/* Only multi-letter extensions are split by underscores */
>>  		if (strnlen(riscv_isa_ext[i].name, 2) != 1)
>>  			seq_puts(f, "_");
>> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
>> index c5b13f7dd482..8e10b50120e9 100644
>> --- a/arch/riscv/kernel/cpufeature.c
>> +++ b/arch/riscv/kernel/cpufeature.c
>> @@ -113,23 +113,29 @@ static bool riscv_isa_extension_check(int id)
>>  	return true;
>>  }
>>  
>> -#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) {	\
>> +#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size, _successor) {	\
>>  	.name = #_name,								\
>>  	.property = #_name,							\
>>  	.id = _id,								\
>>  	.subset_ext_ids = _subset_exts,						\
>> -	.subset_ext_size = _subset_exts_size					\
>> +	.subset_ext_size = _subset_exts_size,					\
>> +	.successor_id = _successor,						\
>>  }
>>  
>> -#define __RISCV_ISA_EXT_DATA(_name, _id) _RISCV_ISA_EXT_DATA(_name, _id, NULL, 0)
>> +#define __RISCV_ISA_EXT_DATA(_name, _id) \
>> +	_RISCV_ISA_EXT_DATA(_name, _id, NULL, 0, RISCV_ISA_EXT_INVALID)
>>  
>>  /* Used to declare pure "lasso" extension (Zk for instance) */
>>  #define __RISCV_ISA_EXT_BUNDLE(_name, _bundled_exts) \
>> -	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, _bundled_exts, ARRAY_SIZE(_bundled_exts))
>> +	_RISCV_ISA_EXT_DATA(_name, RISCV_ISA_EXT_INVALID, \
>> +			    _bundled_exts, ARRAY_SIZE(_bundled_exts), RISCV_ISA_EXT_INVALID)
>>  
>>  /* Used to declare extensions that are a superset of other extensions (Zvbb for instance) */
>>  #define __RISCV_ISA_EXT_SUPERSET(_name, _id, _sub_exts) \
>> -	_RISCV_ISA_EXT_DATA(_name, _id, _sub_exts, ARRAY_SIZE(_sub_exts))
>> +	_RISCV_ISA_EXT_DATA(_name, _id, _sub_exts, ARRAY_SIZE(_sub_exts), RISCV_ISA_EXT_INVALID)
>> +
>> +#define __RISCV_ISA_EXT_VERSION(_name, _id, _preds, _preds_size, _successor) \
>> +	_RISCV_ISA_EXT_DATA(_name, _id, _preds, _preds_size, _successor)
>>  
>>  static const unsigned int riscv_zk_bundled_exts[] = {
>>  	RISCV_ISA_EXT_ZBKB,
>> @@ -201,6 +207,16 @@ static const unsigned int riscv_zvbb_exts[] = {
>>  	RISCV_ISA_EXT_ZVKB
>>  };
>>  
>> +static const unsigned int riscv_sm_ext_versions[] = {
>> +	RISCV_ISA_EXT_SM1p11,
>> +	RISCV_ISA_EXT_SM1p12,
>> +};
>> +
>> +static const unsigned int riscv_ss_ext_versions[] = {
>> +	RISCV_ISA_EXT_SS1p11,
>> +	RISCV_ISA_EXT_SS1p12,
>> +};
>> +
>>  /*
>>   * The canonical order of ISA extension names in the ISA string is defined in
>>   * chapter 27 of the unprivileged specification.
>> @@ -299,8 +315,16 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>>  	__RISCV_ISA_EXT_DATA(zvksh, RISCV_ISA_EXT_ZVKSH),
>>  	__RISCV_ISA_EXT_BUNDLE(zvksg, riscv_zvksg_bundled_exts),
>>  	__RISCV_ISA_EXT_DATA(zvkt, RISCV_ISA_EXT_ZVKT),
>> +	__RISCV_ISA_EXT_VERSION(sm1p11, RISCV_ISA_EXT_SM1p11, riscv_sm_ext_versions, 0,
>> +				RISCV_ISA_EXT_SM1p12),
>> +	__RISCV_ISA_EXT_VERSION(sm1p12, RISCV_ISA_EXT_SM1p12, riscv_sm_ext_versions, 1,
>> +				RISCV_ISA_EXT_INVALID),
>>  	__RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
>>  	__RISCV_ISA_EXT_DATA(smstateen, RISCV_ISA_EXT_SMSTATEEN),
>> +	__RISCV_ISA_EXT_VERSION(ss1p11, RISCV_ISA_EXT_SS1p11, riscv_ss_ext_versions, 0,
>> +				RISCV_ISA_EXT_SS1p12),
>> +	__RISCV_ISA_EXT_VERSION(ss1p12, RISCV_ISA_EXT_SS1p12, riscv_ss_ext_versions, 1,
>> +				RISCV_ISA_EXT_INVALID),
>>  	__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),
>> @@ -414,6 +438,14 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
>>  				;
>>  
>>  			++ext_end;
>> +
>> +			/*
>> +			 * As a special case for the Sm and Ss extensions, where the version
>> +			 * number is important, include it in the extension name.
>> +			 */
>> +			if (ext_end - ext == 2 && tolower(ext[0]) == 's' &&
>> +			    (tolower(ext[1]) == 'm' || tolower(ext[1]) == 's'))
>> +				ext_end = isa;
>>  			break;
>>  		default:
>>  			/*
> 
> 
> Hmm, looking at all of this (especially this hack to the "old" parser),
> I feel more like these should be promoted to a property of their own.
> The "old" parser was designed to handle numbers, and here when you're
> interested in the values behind the numbers (which is a first iirc), you
> don't make any use of that. I don't really want to see a world where

I had a version of this code that parsed the numbers and stored them as integers
in `struct riscv_isainfo`. It didn't work with of_property_match_string() as
used for riscv,isa-extensions, since that function expects the extension name to
be the full string. Either we would need to change the code to parse a version
number out of each string in the riscv,isa-extensions list (and make the binding
a bunch of regexes), or we need a separate "extension" entry (and DT binding
entry) for each supported version.

I chose the second option, and as a consequence I didn't actually need to parse
the integer value in the ISA string code path either.

> we have every single iteration of smNpM under the sun in the property,
> because there's a fair bit of churn in the isa. Granted, this applies to
> all the various, the difference for me is the level of churn.

Indeed. In fact, one thought I had while looking at this code is that we should
be ignoring any extension in the ISA string with a version < 1.0 or >= 2.0,
since those won't be compatible with what we expect.

> Or maybe we can still with the properties you have, but instead of
> treating them like any other extension, handle these separately,
> focusing on the numbering, so that only having the exact version
> supported by a cpu is possible.

Maybe I'm misunderstanding what you're saying here, but it is already the case
that the DT for a CPU would only contain the exact version of the privileged ISA
supported by that CPU.

With this implementation, the fact that the integer version gets expanded to a
series of flags is supposed to be invisible in the DT and to userspace. I
realize I don't quite succeed there: putting "ss1p13" in the ISA string should
work, but does not.

> I'm still pretty undecided, I'd like to think about this a little bit,
> but I think we can do better here.

Sure, no problem. I'm happy to implement whatever we agree on. Though one
consideration I had is that this is all in support of fixing a bug in v6.7, so I
wanted the changes to be backportable.

I suppose the easy way out for backporting is to check for RISCV_ISA_EXT_ZICBOZ
for now, and then solve the larger problem once there is some other user of the
envcfg CSR (or another Ss1p12 feature).

Regards,
Samuel