Re: [PATCH v4 02/11] riscv: add ISA extensions validation

[Conor Dooley]

On Mon, Apr 29, 2024 at 05:04:55PM +0200, Clément Léger wrote:
> Since a few extensions (Zicbom/Zicboz) already needs validation and
> future ones will need it as well (Zc*) add a validate() callback to
> struct riscv_isa_ext_data. This require to rework the way extensions are
> parsed and split it in two phases. First phase is isa string or isa
> extension list parsing and consists in enabling all the extensions in a
> temporary bitmask without any validation. The second step "resolves" the
> final isa bitmap, handling potential missing dependencies. The mechanism
> is quite simple and simply validate each extension described in the
> temporary bitmap before enabling it in the final isa bitmap. validate()
> callbacks can return either 0 for success, -EPROBEDEFER if extension
> needs to be validated again at next loop. A previous ISA bitmap is kept
> to avoid looping mutliple times if an extension dependencies are never
> satisfied until we reach a stable state. In order to avoid any potential
> infinite looping, allow looping a maximum of the number of extension we
> handle. Zicboz and Zicbom extensions are modified to use this validation
> mechanism.

Your reply to my last review only talked about part of my comments,
which is usually what you do when you're gonna implement the rest, but
you haven't.
I like the change you've made to shorten looping, but I'd at least like
a response to why a split is not worth doing :)

Thanks,
Conor.

> 
> Signed-off-by: Clément Léger <cleger@xxxxxxxxxxxx>
> ---
>  arch/riscv/include/asm/cpufeature.h |   1 +
>  arch/riscv/kernel/cpufeature.c      | 211 ++++++++++++++++------------
>  2 files changed, 126 insertions(+), 86 deletions(-)
> 
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index 347805446151..000796c2d0b1 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -70,6 +70,7 @@ struct riscv_isa_ext_data {
>  	const char *property;
>  	const unsigned int *subset_ext_ids;
>  	const unsigned int subset_ext_size;
> +	int (*validate)(const struct riscv_isa_ext_data *data, const unsigned long *isa_bitmap);
>  };
>  
>  extern const struct riscv_isa_ext_data riscv_isa_ext[];
> diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
> index 115ba001f1bc..cb2ffa6c8c33 100644
> --- a/arch/riscv/kernel/cpufeature.c
> +++ b/arch/riscv/kernel/cpufeature.c
> @@ -72,51 +72,58 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, unsigned i
>  }
>  EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
>  
> -static bool riscv_isa_extension_check(int id)
> +static bool riscv_isa_extension_valid(int id)
>  {
> -	switch (id) {
> -	case RISCV_ISA_EXT_ZICBOM:
> -		if (!riscv_cbom_block_size) {
> -			pr_err("Zicbom detected in ISA string, disabling as no cbom-block-size found\n");
> -			return false;
> -		} else if (!is_power_of_2(riscv_cbom_block_size)) {
> -			pr_err("Zicbom disabled as cbom-block-size present, but is not a power-of-2\n");
> -			return false;
> -		}
> -		return true;
> -	case RISCV_ISA_EXT_ZICBOZ:
> -		if (!riscv_cboz_block_size) {
> -			pr_err("Zicboz detected in ISA string, disabling as no cboz-block-size found\n");
> -			return false;
> -		} else if (!is_power_of_2(riscv_cboz_block_size)) {
> -			pr_err("Zicboz disabled as cboz-block-size present, but is not a power-of-2\n");
> -			return false;
> -		}
> -		return true;
> -	case RISCV_ISA_EXT_INVALID:
> -		return false;
> +	return id != RISCV_ISA_EXT_INVALID;
> +}
> +
> +static int riscv_ext_zicbom_validate(const struct riscv_isa_ext_data *data,
> +				     const unsigned long *isa_bitmap)
> +{
> +	if (!riscv_cbom_block_size) {
> +		pr_err("Zicbom detected in ISA string, disabling as no cbom-block-size found\n");
> +		return -EINVAL;
> +	} else if (!is_power_of_2(riscv_cbom_block_size)) {
> +		pr_err("Zicbom disabled as cbom-block-size present, but is not a power-of-2\n");
> +		return -EINVAL;
>  	}
> +	return 0;
> +}
>  
> -	return true;
> +static int riscv_ext_zicboz_validate(const struct riscv_isa_ext_data *data,
> +				     const unsigned long *isa_bitmap)
> +{
> +	if (!riscv_cboz_block_size) {
> +		pr_err("Zicboz detected in ISA string, disabling as no cboz-block-size found\n");
> +		return -EINVAL;
> +	} else if (!is_power_of_2(riscv_cboz_block_size)) {
> +		pr_err("Zicboz disabled as cboz-block-size present, but is not a power-of-2\n");
> +		return -EINVAL;
> +	}
> +	return 0;
>  }
>  
> -#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size) {	\
> -	.name = #_name,								\
> -	.property = #_name,							\
> -	.id = _id,								\
> -	.subset_ext_ids = _subset_exts,						\
> -	.subset_ext_size = _subset_exts_size					\
> +#define _RISCV_ISA_EXT_DATA(_name, _id, _subset_exts, _subset_exts_size, _validate) {	\
> +	.name = #_name,									\
> +	.property = #_name,								\
> +	.id = _id,									\
> +	.subset_ext_ids = _subset_exts,							\
> +	.subset_ext_size = _subset_exts_size,						\
> +	.validate = _validate								\
>  }
>  
> -#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, NULL)
>  
>  /* 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), NULL)
>  
>  /* 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), NULL)
> +#define __RISCV_ISA_EXT_SUPERSET_VALIDATE(_name, _id, _sub_exts, _validate) \
> +	_RISCV_ISA_EXT_DATA(_name, _id, _sub_exts, ARRAY_SIZE(_sub_exts), _validate)
>  
>  static const unsigned int riscv_zk_bundled_exts[] = {
>  	RISCV_ISA_EXT_ZBKB,
> @@ -247,8 +254,10 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  	__RISCV_ISA_EXT_DATA(c, RISCV_ISA_EXT_c),
>  	__RISCV_ISA_EXT_DATA(v, RISCV_ISA_EXT_v),
>  	__RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
> -	__RISCV_ISA_EXT_SUPERSET(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts),
> -	__RISCV_ISA_EXT_SUPERSET(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts),
> +	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts,
> +					  riscv_ext_zicbom_validate),
> +	__RISCV_ISA_EXT_SUPERSET_VALIDATE(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts,
> +					  riscv_ext_zicboz_validate),
>  	__RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
>  	__RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
>  	__RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
> @@ -310,33 +319,80 @@ const struct riscv_isa_ext_data riscv_isa_ext[] = {
>  
>  const size_t riscv_isa_ext_count = ARRAY_SIZE(riscv_isa_ext);
>  
> -static void __init match_isa_ext(const struct riscv_isa_ext_data *ext, const char *name,
> -				 const char *name_end, struct riscv_isainfo *isainfo)
> +static void riscv_isa_set_ext(const struct riscv_isa_ext_data *ext, unsigned long *bitmap)
>  {
> -	if ((name_end - name == strlen(ext->name)) &&
> -	     !strncasecmp(name, ext->name, name_end - name)) {
> -		/*
> -		 * If this is a bundle, enable all the ISA extensions that
> -		 * comprise the bundle.
> -		 */
> -		if (ext->subset_ext_size) {
> -			for (int i = 0; i < ext->subset_ext_size; i++) {
> -				if (riscv_isa_extension_check(ext->subset_ext_ids[i]))
> -					set_bit(ext->subset_ext_ids[i], isainfo->isa);
> -			}
> +	/*
> +	 * This is valid even for bundle extensions which uses the RISCV_ISA_EXT_INVALID id
> +	 * (rejected by riscv_isa_extension_valid()).
> +	 */
> +	if (riscv_isa_extension_valid(ext->id))
> +		set_bit(ext->id, bitmap);
> +
> +	for (int i = 0; i < ext->subset_ext_size; i++) {
> +		if (riscv_isa_extension_valid(ext->subset_ext_ids[i]))
> +			set_bit(ext->subset_ext_ids[i], bitmap);
> +	}
> +}
> +
> +static void __init riscv_resolve_isa(unsigned long *isa_bitmap, struct riscv_isainfo *isainfo,
> +				     unsigned long *this_hwcap, unsigned long *isa2hwcap)
> +{
> +	bool loop;
> +	const struct riscv_isa_ext_data *ext;
> +	DECLARE_BITMAP(prev_bitmap, RISCV_ISA_EXT_MAX);
> +	int max_loop_count = riscv_isa_ext_count, ret;
> +
> +	do {
> +		loop = false;
> +		if (max_loop_count-- < 0) {
> +			pr_err("Failed to reach a stable ISA state\n");
> +			return;
>  		}
> +		memcpy(prev_bitmap, isainfo->isa, sizeof(prev_bitmap));
> +		for (int i = 0; i < riscv_isa_ext_count; i++) {
> +			ext = &riscv_isa_ext[i];
> +
> +			/* Bundle extensions ids are invalid*/
> +			if (!riscv_isa_extension_valid(ext->id))
> +				continue;
> +
> +			if (!test_bit(ext->id, isa_bitmap) || test_bit(ext->id, isainfo->isa))
> +				continue;
> +
> +			if (ext->validate) {
> +				ret = ext->validate(ext, isainfo->isa);
> +				if (ret) {
> +					if (ret == -EPROBE_DEFER)
> +						loop = true;
> +					else
> +						clear_bit(ext->id, isa_bitmap);
> +					continue;
> +				}
> +			}
>  
> -		/*
> -		 * This is valid even for bundle extensions which uses the RISCV_ISA_EXT_INVALID id
> -		 * (rejected by riscv_isa_extension_check()).
> -		 */
> -		if (riscv_isa_extension_check(ext->id))
>  			set_bit(ext->id, isainfo->isa);
> +
> +			/* Only single letter extensions get set in hwcap */
> +			if (ext->id < RISCV_ISA_EXT_BASE)
> +				*this_hwcap |= isa2hwcap[ext->id];
> +		}
> +	} while (loop && memcmp(prev_bitmap, isainfo->isa, sizeof(prev_bitmap)));
> +}
> +
> +static void __init match_isa_ext(const char *name, const char *name_end, unsigned long *bitmap)
> +{
> +	for (int i = 0; i < riscv_isa_ext_count; i++) {
> +		const struct riscv_isa_ext_data *ext = &riscv_isa_ext[i];
> +
> +		if ((name_end - name == strlen(ext->name)) &&
> +		    !strncasecmp(name, ext->name, name_end - name)) {
> +			riscv_isa_set_ext(ext, bitmap);
> +			break;
> +		}
>  	}
>  }
>  
> -static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct riscv_isainfo *isainfo,
> -					  unsigned long *isa2hwcap, const char *isa)
> +static void __init riscv_resolve_isa_string(const char *isa, unsigned long *bitmap)
>  {
>  	/*
>  	 * For all possible cpus, we have already validated in
> @@ -349,7 +405,7 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
>  	while (*isa) {
>  		const char *ext = isa++;
>  		const char *ext_end = isa;
> -		bool ext_long = false, ext_err = false;
> +		bool ext_err = false;
>  
>  		switch (*ext) {
>  		case 's':
> @@ -389,7 +445,6 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
>  			 * character itself while eliminating the extensions version number.
>  			 * A simple re-increment solves this problem.
>  			 */
> -			ext_long = true;
>  			for (; *isa && *isa != '_'; ++isa)
>  				if (unlikely(!isalnum(*isa)))
>  					ext_err = true;
> @@ -469,17 +524,8 @@ static void __init riscv_parse_isa_string(unsigned long *this_hwcap, struct risc
>  
>  		if (unlikely(ext_err))
>  			continue;
> -		if (!ext_long) {
> -			int nr = tolower(*ext) - 'a';
>  
> -			if (riscv_isa_extension_check(nr)) {
> -				*this_hwcap |= isa2hwcap[nr];
> -				set_bit(nr, isainfo->isa);
> -			}
> -		} else {
> -			for (int i = 0; i < riscv_isa_ext_count; i++)
> -				match_isa_ext(&riscv_isa_ext[i], ext, ext_end, isainfo);
> -		}
> +		match_isa_ext(ext, ext_end, bitmap);
>  	}
>  }
>  
> @@ -501,6 +547,7 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  	for_each_possible_cpu(cpu) {
>  		struct riscv_isainfo *isainfo = &hart_isa[cpu];
>  		unsigned long this_hwcap = 0;
> +		DECLARE_BITMAP(isa_bitmap, RISCV_ISA_EXT_MAX) = { 0 };
>  
>  		if (acpi_disabled) {
>  			node = of_cpu_device_node_get(cpu);
> @@ -523,7 +570,7 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  			}
>  		}
>  
> -		riscv_parse_isa_string(&this_hwcap, isainfo, isa2hwcap, isa);
> +		riscv_resolve_isa_string(isa, isa_bitmap);
>  
>  		/*
>  		 * These ones were as they were part of the base ISA when the
> @@ -531,10 +578,10 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  		 * unconditionally where `i` is in riscv,isa on DT systems.
>  		 */
>  		if (acpi_disabled) {
> -			set_bit(RISCV_ISA_EXT_ZICSR, isainfo->isa);
> -			set_bit(RISCV_ISA_EXT_ZIFENCEI, isainfo->isa);
> -			set_bit(RISCV_ISA_EXT_ZICNTR, isainfo->isa);
> -			set_bit(RISCV_ISA_EXT_ZIHPM, isainfo->isa);
> +			set_bit(RISCV_ISA_EXT_ZICSR, isa_bitmap);
> +			set_bit(RISCV_ISA_EXT_ZIFENCEI, isa_bitmap);
> +			set_bit(RISCV_ISA_EXT_ZICNTR, isa_bitmap);
> +			set_bit(RISCV_ISA_EXT_ZIHPM, isa_bitmap);
>  		}
>  
>  		/*
> @@ -548,9 +595,11 @@ static void __init riscv_fill_hwcap_from_isa_string(unsigned long *isa2hwcap)
>  		if (acpi_disabled && riscv_cached_mvendorid(cpu) == THEAD_VENDOR_ID &&
>  		    riscv_cached_marchid(cpu) == 0x0) {
>  			this_hwcap &= ~isa2hwcap[RISCV_ISA_EXT_v];
> -			clear_bit(RISCV_ISA_EXT_v, isainfo->isa);
> +			clear_bit(RISCV_ISA_EXT_v, isa_bitmap);
>  		}
>  
> +		riscv_resolve_isa(isa_bitmap, isainfo, &this_hwcap, isa2hwcap);
> +
>  		/*
>  		 * All "okay" hart should have same isa. Set HWCAP based on
>  		 * common capabilities of every "okay" hart, in case they don't
> @@ -579,6 +628,7 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
>  		unsigned long this_hwcap = 0;
>  		struct device_node *cpu_node;
>  		struct riscv_isainfo *isainfo = &hart_isa[cpu];
> +		DECLARE_BITMAP(isa_bitmap, RISCV_ISA_EXT_MAX) = { 0 };
>  
>  		cpu_node = of_cpu_device_node_get(cpu);
>  		if (!cpu_node) {
> @@ -598,22 +648,11 @@ static int __init riscv_fill_hwcap_from_ext_list(unsigned long *isa2hwcap)
>  						     ext->property) < 0)
>  				continue;
>  
> -			if (ext->subset_ext_size) {
> -				for (int j = 0; j < ext->subset_ext_size; j++) {
> -					if (riscv_isa_extension_check(ext->subset_ext_ids[i]))
> -						set_bit(ext->subset_ext_ids[j], isainfo->isa);
> -				}
> -			}
> -
> -			if (riscv_isa_extension_check(ext->id)) {
> -				set_bit(ext->id, isainfo->isa);
> -
> -				/* Only single letter extensions get set in hwcap */
> -				if (strnlen(riscv_isa_ext[i].name, 2) == 1)
> -					this_hwcap |= isa2hwcap[riscv_isa_ext[i].id];
> -			}
> +			riscv_isa_set_ext(ext, isa_bitmap);
>  		}
>  
> +		riscv_resolve_isa(isa_bitmap, isainfo, &this_hwcap, isa2hwcap);
> +
>  		of_node_put(cpu_node);
>  
>  		/*
> -- 
> 2.43.0
>

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