Date: Mon, 10 Jun 2024 10:23:49 +0200
From: Clément Léger <cleger@...osinc.com>
To: Charlie Jenkins <charlie@...osinc.com>, Jesse Taube <jesse@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, Paul Walmsley
 <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>,
 Albert Ou <aou@...s.berkeley.edu>, Conor Dooley
 <conor.dooley@...rochip.com>, Evan Green <evan@...osinc.com>,
 Andrew Jones <ajones@...tanamicro.com>, Xiao Wang <xiao.w.wang@...el.com>,
 Andy Chiu <andy.chiu@...ive.com>, Greentime Hu <greentime.hu@...ive.com>,
 Heiko Stuebner <heiko@...ech.de>, Guo Ren <guoren@...nel.org>,
 Björn Töpel <bjorn@...osinc.com>,
 Costa Shulyupin <costa.shul@...hat.com>,
 Andrew Morton <akpm@...ux-foundation.org>, Baoquan He <bhe@...hat.com>,
 Sami Tolvanen <samitolvanen@...gle.com>, Zong Li <zong.li@...ive.com>,
 Ben Dooks <ben.dooks@...ethink.co.uk>, Erick Archer <erick.archer@....com>,
 Vincent Chen <vincent.chen@...ive.com>,
 Joel Granados <j.granados@...sung.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] RISC-V: Detect unaligned vector accesses supported.



On 06/06/2024 23:29, Charlie Jenkins wrote:
> On Thu, Jun 06, 2024 at 02:32:14PM -0400, Jesse Taube wrote:
>> Run a unaligned vector access to test if the system supports
>> vector unaligned access. Add the result to a new key in hwprobe.
>> This is useful for usermode to know if vector misaligned accesses are
>> supported and if they are faster or slower than equivalent byte accesses.
>>
>> Signed-off-by: Jesse Taube <jesse@...osinc.com>
>> ---
>>  arch/riscv/include/asm/cpufeature.h        |  2 +
>>  arch/riscv/include/asm/hwprobe.h           |  2 +-
>>  arch/riscv/include/asm/vector.h            |  1 +
>>  arch/riscv/include/uapi/asm/hwprobe.h      |  6 ++
>>  arch/riscv/kernel/sys_hwprobe.c            | 34 +++++++++
>>  arch/riscv/kernel/traps_misaligned.c       | 84 ++++++++++++++++++++--
>>  arch/riscv/kernel/unaligned_access_speed.c |  4 ++
>>  arch/riscv/kernel/vector.c                 |  2 +-
>>  8 files changed, 129 insertions(+), 6 deletions(-)
>>
>> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
>> index 347805446151..a012c8490a27 100644
>> --- a/arch/riscv/include/asm/cpufeature.h
>> +++ b/arch/riscv/include/asm/cpufeature.h
>> @@ -35,9 +35,11 @@ void riscv_user_isa_enable(void);
>>  
>>  #if defined(CONFIG_RISCV_MISALIGNED)
>>  bool check_unaligned_access_emulated_all_cpus(void);
>> +bool check_vector_unaligned_access_all_cpus(void);
>>  void unaligned_emulation_finish(void);
>>  bool unaligned_ctl_available(void);
>>  DECLARE_PER_CPU(long, misaligned_access_speed);
>> +DECLARE_PER_CPU(long, vector_misaligned_access);
>>  #else
>>  static inline bool unaligned_ctl_available(void)
>>  {
>> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
>> index 630507dff5ea..150a9877b0af 100644
>> --- a/arch/riscv/include/asm/hwprobe.h
>> +++ b/arch/riscv/include/asm/hwprobe.h
>> @@ -8,7 +8,7 @@
>>  
>>  #include <uapi/asm/hwprobe.h>
>>  
>> -#define RISCV_HWPROBE_MAX_KEY 6
>> +#define RISCV_HWPROBE_MAX_KEY 7
>>  
>>  static inline bool riscv_hwprobe_key_is_valid(__s64 key)
>>  {
>> diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h
>> index 731dcd0ed4de..776af9b37e23 100644
>> --- a/arch/riscv/include/asm/vector.h
>> +++ b/arch/riscv/include/asm/vector.h
>> @@ -21,6 +21,7 @@
>>  
>>  extern unsigned long riscv_v_vsize;
>>  int riscv_v_setup_vsize(void);
>> +bool insn_is_vector(u32 insn_buf);
>>  bool riscv_v_first_use_handler(struct pt_regs *regs);
>>  void kernel_vector_begin(void);
>>  void kernel_vector_end(void);
>> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
>> index 060212331a03..ebacff86f134 100644
>> --- a/arch/riscv/include/uapi/asm/hwprobe.h
>> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
>> @@ -68,6 +68,12 @@ struct riscv_hwprobe {
>>  #define		RISCV_HWPROBE_MISALIGNED_UNSUPPORTED	(4 << 0)
>>  #define		RISCV_HWPROBE_MISALIGNED_MASK		(7 << 0)
>>  #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE	6
>> +#define RISCV_HWPROBE_VEC_KEY_MISALIGNED_PERF	7
>> +#define		RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN		0
>> +#define		RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED		1
>> +#define		RISCV_HWPROBE_VEC_MISALIGNED_SLOW		2
>> +#define		RISCV_HWPROBE_VEC_MISALIGNED_FAST		3
>> +#define		RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED	4
>>  /* Increase RISCV_HWPROBE_MAX_KEY when adding items. */
>>  
>>  /* Flags */
>> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
>> index b286b73e763e..ce641cc6e47a 100644
>> --- a/arch/riscv/kernel/sys_hwprobe.c
>> +++ b/arch/riscv/kernel/sys_hwprobe.c
>> @@ -184,6 +184,36 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus)
>>  }
>>  #endif
>>  
>> +#if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS)
>> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>> +{
>> +	int cpu;
>> +	u64 perf = -1ULL;
>> +
>> +	for_each_cpu(cpu, cpus) {
>> +		int this_perf = per_cpu(vector_misaligned_access, cpu);
>> +
>> +		if (perf == -1ULL)
>> +			perf = this_perf;
>> +
>> +		if (perf != this_perf) {
>> +			perf = RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>> +			break;
>> +		}
>> +	}
>> +
>> +	if (perf == -1ULL)
>> +		return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>> +
>> +	return perf;
>> +}
>> +#else
>> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>> +{
>> +	return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>> +}
>> +#endif
>> +
>>  static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>  			     const struct cpumask *cpus)
>>  {
>> @@ -211,6 +241,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>  		pair->value = hwprobe_misaligned(cpus);
>>  		break;
>>  
>> +	case RISCV_HWPROBE_VEC_KEY_MISALIGNED_PERF:
>> +		pair->value = hwprobe_vec_misaligned(cpus);
>> +		break;
>> +
>>  	case RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE:
>>  		pair->value = 0;
>>  		if (hwprobe_ext0_has(cpus, RISCV_HWPROBE_EXT_ZICBOZ))
>> diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
>> index 2adb7c3e4dd5..8f26c3d92230 100644
>> --- a/arch/riscv/kernel/traps_misaligned.c
>> +++ b/arch/riscv/kernel/traps_misaligned.c
>> @@ -16,6 +16,7 @@
>>  #include <asm/entry-common.h>
>>  #include <asm/hwprobe.h>
>>  #include <asm/cpufeature.h>
>> +#include <asm/vector.h>
>>  
>>  #define INSN_MATCH_LB			0x3
>>  #define INSN_MASK_LB			0x707f
>> @@ -413,10 +414,6 @@ int handle_misaligned_load(struct pt_regs *regs)
>>  
>>  	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
>>  
>> -#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>> -	*this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED;
>> -#endif
>> -
>>  	if (!unaligned_enabled)
>>  		return -1;
>>  
>> @@ -426,6 +423,17 @@ int handle_misaligned_load(struct pt_regs *regs)
>>  	if (get_insn(regs, epc, &insn))
>>  		return -1;
>>  
>> +#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>> +	if (insn_is_vector(insn) &&
>> +	    *this_cpu_ptr(&vector_misaligned_access) == RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED) {
>> +		*this_cpu_ptr(&vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>> +		regs->epc = epc + INSN_LEN(insn);
>> +		return 0;
>> +	}
>> +
>> +	*this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED;
> 
> This unconditionally sets scalar unaligned accesses even if the
> unaligned access is caused by vector. Scalar unaligned accesses should
> only be set to emulated if this function is entered from a scalar
> unaligned load.
> 
> The rest of this function handles how scalar unaligned accesses are
> emulated, and the equivalent needs to happen for vector. You need to add
> routines that manually load the data from the memory address into the
> vector register. When Clément did this for scalar, he provided a test
> case to help reviewers [1]. Please add onto these test cases or make
> your own for vector.
> 
> Link: https://github.com/clementleger/unaligned_test [1]

Hi Jesse,

I already mentionned that in a previous message and got no answer [1].
Please address all feedback before sending another version. Adding a
cover letter for such series would also be appreciated.

Thanks,

Clément

Link :https://lore.kernel.org/all/2c355b76-c768-46b1-9f37
fd1991a54bfd@...osinc.com/ [1]

> 
>> +#endif
>> +
>>  	regs->epc = 0;
>>  
>>  	if ((insn & INSN_MASK_LW) == INSN_MATCH_LW) {
>> @@ -625,6 +633,74 @@ static bool check_unaligned_access_emulated(int cpu)
>>  	return misaligned_emu_detected;
>>  }
>>  
>> +#ifdef CONFIG_RISCV_ISA_V
>> +static void check_vector_unaligned_access(struct work_struct *unused)
> 
> Can you standardize this name with the scalar version by writing
> emulated in it?
> 
> "check_vector_unaligned_access_emulated_all_cpus"
> 
>> +{
>> +	int cpu = smp_processor_id();
>> +	long *mas_ptr = this_cpu_ptr(&vector_misaligned_access);
>> +	unsigned long tmp_var;
>> +
>> +	if (!riscv_isa_extension_available(hart_isa[cpu].isa, v))
>> +		return;
>> +
>> +	*mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>> +
>> +	local_irq_enable();
>> +	kernel_vector_begin();
>> +	__asm__ __volatile__ (
>> +		".balign 4\n\t"
>> +		".option push\n\t"
>> +		".option arch, +v\n\t"
>> +		"       vsetivli zero, 1, e16, m1, ta, ma\n\t"	// Vectors of 16b
>> +		"	vle16.v v0, (%[ptr])\n\t"		// Load bytes
>> +		".option pop\n\t"
>> +		: : [ptr] "r" ((u8 *)&tmp_var + 1) : "v0", "memory");
> 
> memory is being read from, but not written to, so there is no need to
> have a memory clobber.
> 
>> +	kernel_vector_end();
>> +
>> +	if (*mas_ptr == RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN)
>> +		*mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>> +}
>> +
>> +bool check_vector_unaligned_access_all_cpus(void)
>> +{
>> +	int cpu;
>> +	bool ret = true;
>> +
>> +	for_each_online_cpu(cpu)
>> +		if (riscv_isa_extension_available(hart_isa[cpu].isa, ZICCLSM))
> 
> zicclsm is not specific to vector so it can be extracted out of this
> vector specific function. Assuming that hardware properly reports the
> extension, if zicclsm is present then it is known that both vector and
> scalar unaligned accesses are supported.
> 
>> +			per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
> 
> Please use the exising UNKNOWN terminology instead of renaming to
> SUPPORTED. Any option that is not UNSUPPORTED implies that unaligned
> accesses are supported.
> 
>> +		else
>> +			ret = false;
>> +
>> +
>> +	if (ret)
>> +		return true;
>> +	ret = true;
>> +
>> +	schedule_on_each_cpu(check_vector_unaligned_access);
>> +
>> +	for_each_online_cpu(cpu)
>> +		if (per_cpu(vector_misaligned_access, cpu)
>> +		    != RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED)
>> +			return false;
>> +
>> +	return ret;
>> +}
>> +#else
> 
> If CONFIG_RISCV_ISA_V is not set, there is no value in checking if
> vector unaligned accesses are supported because userspace will not be
> allowed to use vector instructions anyway.
> 
> - Charlie
> 
>> +bool check_vector_unaligned_access_all_cpus(void)
>> +{
>> +	int cpu;
>> +
>> +	for_each_online_cpu(cpu)
>> +		if (riscv_isa_extension_available(hart_isa[cpu].isa, ZICCLSM))
>> +			per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_SUPPORTED;
>> +		else
>> +			per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>> +
>> +	return false;
>> +}
>> +#endif
>> +
>>  bool check_unaligned_access_emulated_all_cpus(void)
>>  {
>>  	int cpu;
>> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
>> index a9a6bcb02acf..92a84239beaa 100644
>> --- a/arch/riscv/kernel/unaligned_access_speed.c
>> +++ b/arch/riscv/kernel/unaligned_access_speed.c
>> @@ -20,6 +20,7 @@
>>  #define MISALIGNED_COPY_SIZE ((MISALIGNED_BUFFER_SIZE / 2) - 0x80)
>>  
>>  DEFINE_PER_CPU(long, misaligned_access_speed);
>> +DEFINE_PER_CPU(long, vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>  
>>  #ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>  static cpumask_t fast_misaligned_access;
>> @@ -264,6 +265,8 @@ static int check_unaligned_access_all_cpus(void)
>>  {
>>  	bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
>>  
>> +	check_vector_unaligned_access_all_cpus();
>> +
>>  	if (!all_cpus_emulated)
>>  		return check_unaligned_access_speed_all_cpus();
>>  
>> @@ -273,6 +276,7 @@ static int check_unaligned_access_all_cpus(void)
>>  static int check_unaligned_access_all_cpus(void)
>>  {
>>  	check_unaligned_access_emulated_all_cpus();
>> +	check_vector_unaligned_access_all_cpus();
>>  
>>  	return 0;
>>  }
>> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
>> index 6727d1d3b8f2..2cceab739b2c 100644
>> --- a/arch/riscv/kernel/vector.c
>> +++ b/arch/riscv/kernel/vector.c
>> @@ -66,7 +66,7 @@ void __init riscv_v_setup_ctx_cache(void)
>>  #endif
>>  }
>>  
>> -static bool insn_is_vector(u32 insn_buf)
>> +bool insn_is_vector(u32 insn_buf)
>>  {
>>  	u32 opcode = insn_buf & __INSN_OPCODE_MASK;
>>  	u32 width, csr;
>> -- 
>> 2.43.0
>>

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