Re: [PATCH v2 4/6] RISC-V: Detect unaligned vector accesses supported.

Jesse Taube
2024-06-20T23:09:09Z

On 6/20/24 18:14, Charlie Jenkins wrote:
> On Thu, Jun 20, 2024 at 05:31:28PM -0400, Jesse Taube wrote:
>>
>>
>> On 6/17/24 22:09, Charlie Jenkins wrote:
>>> On Mon, Jun 17, 2024 at 06:43:32PM -0700, Charlie Jenkins wrote:
>>>> On Thu, Jun 13, 2024 at 03:16:13PM -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@rivosinc.com>
>>>>> ---
>>>>> V1 -> V2:
>>>>> - Add Kconfig options
>>>>> - Add insn_is_vector
>>>>> - Add handle_vector_misaligned_load
>>>>> - Fix build
>>>>> - Seperate vector from scalar misaligned access
>>>>> - This patch was almost completely rewritten
>>>>> ---
>>>>> arch/riscv/Kconfig | 41 +++++++
>>>>> arch/riscv/include/asm/cpufeature.h | 7 +-
>>>>> arch/riscv/include/asm/entry-common.h | 11 --
>>>>> arch/riscv/include/asm/hwprobe.h | 2 +-
>>>>> arch/riscv/include/asm/vector.h | 1 +
>>>>> arch/riscv/include/uapi/asm/hwprobe.h | 5 +
>>>>> arch/riscv/kernel/Makefile | 4 +-
>>>>> arch/riscv/kernel/sys_hwprobe.c | 41 +++++++
>>>>> arch/riscv/kernel/traps_misaligned.c | 119 ++++++++++++++++++++-
>>>>> arch/riscv/kernel/unaligned_access_speed.c | 9 +-
>>>>> arch/riscv/kernel/vector.c | 2 +-
>>>>> 11 files changed, 221 insertions(+), 21 deletions(-)
>>>>>
>>>>> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
>>>>> index b94176e25be1..f12df0ca6c18 100644
>>>>> --- a/arch/riscv/Kconfig
>>>>> +++ b/arch/riscv/Kconfig
>>>>> @@ -723,6 +723,12 @@ config RISCV_MISALIGNED
>>>>> help
>>>>> Embed support for emulating misaligned loads and stores.
>>>>> +config RISCV_VECTOR_MISALIGNED
>>>>> + bool
>>>>> + depends on RISCV_ISA_V
>>>>> + help
>>>>> + Enable detecting support for vector misaligned loads and stores.
>>>>> +
>>>>> choice
>>>>> prompt "Unaligned Accesses Support"
>>>>> default RISCV_PROBE_UNALIGNED_ACCESS
>>>>> @@ -774,6 +780,41 @@ config RISCV_EFFICIENT_UNALIGNED_ACCESS
>>>>> endchoice
>>>>> +choice
>>>>> + prompt "Vector unaligned Accesses Support"
>>>>> + depends on RISCV_ISA_V
>>>>> + default RISCV_PROBE_VECTOR_UNALIGNED_ACCESS
>>>>> + help
>>>>> + This determines the level of support for vector unaligned accesses. This
>>>>> + information is used by the kernel to perform optimizations. It is also
>>>>> + exposed to user space via the hwprobe syscall. The hardware will be
>>>>> + probed at boot by default.
>>>>> +
>>>>> +config RISCV_DETECT_VECTOR_UNALIGNED_ACCESS
>>>>
>>>> This is not used anywhere, what is the reason for including it?
>>
>> This is so that we can check if they are supported or not, but not check the
>> speed of them. Similar to RISCV_EMULATED_UNALIGNED_ACCESS.
>
> What do you mean? It isn't used anywhere so this "check if they are
> supported or not" is not guarded by this config.

It is not used anywhere because it just needs to enable
RISCV_VECTOR_MISALIGNED and nothing else.

>
>>
>>>>
>>>>> + bool "Detect support for vector unaligned accesses"
>>>>> + select RISCV_VECTOR_MISALIGNED
>>>>> + help
>>>>> + During boot, the kernel will detect if the system supports vector
>>>>> + unaligned accesses.
>>>>> +
>>>>> +config RISCV_PROBE_VECTOR_UNALIGNED_ACCESS
>>>>> + bool "Probe speed of vector unaligned accesses"
>>>>> + select RISCV_VECTOR_MISALIGNED
>>>>> + help
>>>>> + During boot, the kernel will run a series of tests to determine the
>>>>> + speed of vector unaligned accesses if they are supported. This probing
>>>>> + will dynamically determine the speed of vector unaligned accesses on
>>>>> + the underlying system if they are supported.
>>>>> +
>>>>> +config CONFIG_RISCV_UNALIGNED_ACCESS_UNSUPPORTED
>>>>
>>>> This should not be prefixed with CONFIG and does not include VECTOR in
>>>> the name.
>>
>> Huh thought it would warn fixed though
>
> What do you mean by "warn fixed"?

Huh thought it would warn. fixed though.

As in I fixed it in V3.

>
>>
>>> I assume you meant to put
>>>> "RISCV_VEC_UNALIGNED_ACCESS_UNSUPPORTED" here?
>>
>> This is to leave a faster path like SLOW or FAST to say that unaligned
>> access arent suported.
>
> I am not sure what you are responding to. This comment seems to be
> responding to my correction of
> CONFIG_RISCV_UNALIGNED_ACCESS_UNSUPPORTED->RISCV_VEC_UNALIGNED_ACCESS_UNSUPPORTED
> so I don't see how that ties into SLOW/FAST

Sorry for the confustion it was meant respond to the comment below...

>
>>
>>>>
>>>> This was also intentionally left out on the scalar side [1]. The
>>>> implication here is that having this config will cause people to compile
>>>> kernels without unaligned access support which really shouldn't be
>>>> something we are explicitly supporting.
>>>>
>>>> If somebody does want to support hardware that does not handle vector
>>>> unaligned accesses, the solution should be to add emulation support to
>>>> the kernel.
>>
>> Yes but we dont have emulation support yet so I do think its a good idea.
>
> I am hesitant because it is very likely that somebody will add support
> for unaligned vector emulation. When there is emulation support, this
> config option should not exist to be consistent with scalar. However if
> we add this option in now, we must expect a user to enable this config,
> and then we will have to get rid of it later. Users are not always happy
> when config options are removed.

I will remove it then.

>
>>
>>>>
>>>> Link: https://lore.kernel.org/all/Zd4y5llkvTfKHf6b@ghost/ [1]
>>>>
>>>> - Charlie
>>>>
>>>>> + bool "Assume the system does not support vector unaligned memory accesses"
>>>>> + help
>>>>> + Assume that the system does not support vector unaligned memory accesses.
>>>>> + The kernel and userspace programs may run them successfully on systems
>>>>> + that do support vector unaligned memory accesses.
>>>>> +
>>>>> +endchoice
>>>>> +
>>>>> endmenu # "Platform type"
>>>>> menu "Kernel features"
>>>>> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
>>>>> index 347805446151..d0ea5921ab20 100644
>>>>> --- a/arch/riscv/include/asm/cpufeature.h
>>>>> +++ b/arch/riscv/include/asm/cpufeature.h
>>>>> @@ -33,8 +33,8 @@ extern struct riscv_isainfo hart_isa[NR_CPUS];
>>>>> void riscv_user_isa_enable(void);
>>>>> -#if defined(CONFIG_RISCV_MISALIGNED)
>>>>> bool check_unaligned_access_emulated_all_cpus(void);
>>>>> +#if defined(CONFIG_RISCV_MISALIGNED)
>>>>> void unaligned_emulation_finish(void);
>>>>> bool unaligned_ctl_available(void);
>>>>> DECLARE_PER_CPU(long, misaligned_access_speed);
>>>>> @@ -45,6 +45,11 @@ static inline bool unaligned_ctl_available(void)
>>>>> }
>>>>> #endif
>>>>> +bool check_vector_unaligned_access_emulated_all_cpus(void);
>>>>> +#if defined(CONFIG_RISCV_VECTOR_MISALIGNED)
>>>>> +DECLARE_PER_CPU(long, vector_misaligned_access);
>>>>> +#endif
>>>>> +
>>>>> #if defined(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS)
>>>>> DECLARE_STATIC_KEY_FALSE(fast_unaligned_access_speed_key);
>>>>> diff --git a/arch/riscv/include/asm/entry-common.h b/arch/riscv/include/asm/entry-common.h
>>>>> index 2293e535f865..7b32d2b08bb6 100644
>>>>> --- a/arch/riscv/include/asm/entry-common.h
>>>>> +++ b/arch/riscv/include/asm/entry-common.h
>>>>> @@ -25,18 +25,7 @@ static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs,
>>>>> void handle_page_fault(struct pt_regs *regs);
>>>>> void handle_break(struct pt_regs *regs);
>>>>> -#ifdef CONFIG_RISCV_MISALIGNED
>>>>> int handle_misaligned_load(struct pt_regs *regs);
>>>>> int handle_misaligned_store(struct pt_regs *regs);
>>>>> -#else
>>>>> -static inline int handle_misaligned_load(struct pt_regs *regs)
>>>>> -{
>>>>> - return -1;
>>>>> -}
>>>>> -static inline int handle_misaligned_store(struct pt_regs *regs)
>>>>> -{
>>>>> - return -1;
>>>>> -}
>>>>> -#endif
>>>>> #endif /* _ASM_RISCV_ENTRY_COMMON_H */
>>>>> diff --git a/arch/riscv/include/asm/hwprobe.h b/arch/riscv/include/asm/hwprobe.h
>>>>> index 150a9877b0af..ef01c182af2b 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 7
>>>>> +#define RISCV_HWPROBE_MAX_KEY 8
>>>>> 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 be7d309cca8a..99b0f91db9ee 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 023b7771d1b7..2fee870e41bb 100644
>>>>> --- a/arch/riscv/include/uapi/asm/hwprobe.h
>>>>> +++ b/arch/riscv/include/uapi/asm/hwprobe.h
>>>>> @@ -75,6 +75,11 @@ struct riscv_hwprobe {
>>>>> #define RISCV_HWPROBE_MISALIGNED_MASK (7 << 0)
>>>>> #define RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE 6
>>>>> #define RISCV_HWPROBE_KEY_MISALIGNED_PERF 7
>>>>> +#define RISCV_HWPROBE_KEY_VEC_MISALIGNED_PERF 8
>>>>> +#define RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN 0
>>>>
>>>> I appreciate you leaving the key for EMULATED open!
>>>>
>>>>> +#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/Makefile b/arch/riscv/kernel/Makefile
>>>>> index 5b243d46f4b1..62ac19c029f1 100644
>>>>> --- a/arch/riscv/kernel/Makefile
>>>>> +++ b/arch/riscv/kernel/Makefile
>>>>> @@ -62,8 +62,8 @@ obj-y += probes/
>>>>> obj-y += tests/
>>>>> obj-$(CONFIG_MMU) += vdso.o vdso/
>>>>> -obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o
>>>>> -obj-$(CONFIG_RISCV_MISALIGNED) += unaligned_access_speed.o
>>>>> +obj-y += traps_misaligned.o
>>>>> +obj-y += unaligned_access_speed.o
>>
>>> These files only need to be compiled if either CONFIG_RISCV_MISALIGNED
>>> or CONFIG_RISCV_VECTOR_MISALIGNED is selected. Can you refactor this
>>> code to replace CONFIG_RISCV_MISALIGNED with
>>> CONFIG_RISCV_SCALAR_MISALIGNED and then have
>>> CONFIG_RISCV_SCALAR_MISALIGNED and CONFIG_RISCV_VECTOR_MISALIGNED
>>> select CONFIG_RISCV_MISALIGNED in the Kconfig?
>>
>> Fixed!
>>
>>>>> obj-$(CONFIG_RISCV_PROBE_UNALIGNED_ACCESS) += copy-unaligned.o
>>>>> obj-$(CONFIG_FPU) += fpu.o
>>>>> diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
>>>>> index e910e2971984..c40df314058b 100644
>>>>> --- a/arch/riscv/kernel/sys_hwprobe.c
>>>>> +++ b/arch/riscv/kernel/sys_hwprobe.c
>>>>> @@ -194,6 +194,43 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus)
>>>>> }
>>>>> #endif
>>>>> +#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
>>>>> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
>>>>> +{
>>>>> + int cpu;
>>>>> + u64 perf = -1ULL;
>>>>> +
>>>>> + if (IS_ENABLED(CONFIG_RISCV_UNALIGNED_ACCESS_UNSUPPORTED))
>>>>> + return RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>>> +
>>>>> + /* Return if supported or not even if speed wasn't probed */
>>>>> + 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)
>>>>> +{
>>>>> + if (IS_ENABLED(CONFIG_RISCV_UNALIGNED_ACCESS_UNSUPPORTED))
>>>>> + return RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>>> +
>>>>> + return RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>>>> const struct cpumask *cpus)
>>>>> {
>>>>> @@ -222,6 +259,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
>>>>> pair->value = hwprobe_misaligned(cpus);
>>>>> break;
>>>>> + case RISCV_HWPROBE_KEY_VEC_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 8fadbe00dd62..6f0264a8c9de 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
>>>>> @@ -322,12 +323,37 @@ union reg_data {
>>>>> u64 data_u64;
>>>>> };
>>>>> -static bool unaligned_ctl __read_mostly;
>>>>> -
>>>>> /* sysctl hooks */
>>>>> int unaligned_enabled __read_mostly = 1; /* Enabled by default */
>>>>> -int handle_misaligned_load(struct pt_regs *regs)
>>>>> +#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
>>>>> +static int handle_vector_misaligned_load(struct pt_regs *regs)
>>>>> +{
>>>>> + unsigned long epc = regs->epc;
>>>>> + unsigned long insn;
>>>>> +
>>>>> + if (get_insn(regs, epc, &insn))
>>>>> + return -1;
>>>>> +
>>>>> + /* Only return 0 when in check_vector_unaligned_access_emulated */
>>>>> + if (*this_cpu_ptr(&vector_misaligned_access) == RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN) {
>>>>> + *this_cpu_ptr(&vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>>> + regs->epc = epc + INSN_LEN(insn);
>>>>> + return 0;
>>>>> + }
>>>>> +
>>>>> + /* If vector instruction we don't emulate it yet */
>>>>> + regs->epc = epc;
>>>>> + return -1;
>>>>> +}
>>>>> +#else
>>>>> +static int handle_vector_misaligned_load(struct pt_regs *regs)
>>>>> +{
>>>>> + return -1;
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +static int handle_scalar_misaligned_load(struct pt_regs *regs)
>>>>> {
>>>>> union reg_data val;
>>>>> unsigned long epc = regs->epc;
>>>>> @@ -435,7 +461,7 @@ int handle_misaligned_load(struct pt_regs *regs)
>>>>> return 0;
>>>>> }
>>>>> -int handle_misaligned_store(struct pt_regs *regs)
>>>>> +static int handle_scalar_misaligned_store(struct pt_regs *regs)
>>>>> {
>>>>> union reg_data val;
>>>>> unsigned long epc = regs->epc;
>>>>> @@ -526,6 +552,85 @@ int handle_misaligned_store(struct pt_regs *regs)
>>>>> return 0;
>>>>> }
>>>>> +int handle_misaligned_load(struct pt_regs *regs)
>>>>> +{
>>>>> + unsigned long epc = regs->epc;
>>>>> + unsigned long insn;
>>>>> +
>>>>> + if (IS_ENABLED(CONFIG_RISCV_VECTOR_MISALIGNED)) {
>>>>> + if (get_insn(regs, epc, &insn))
>>>>> + return -1;
>>>>> +
>>>>> + if (insn_is_vector(insn))
>>>>> + return handle_vector_misaligned_load(regs);
>>>>> + }
>>>>> +
>>>>> + if (IS_ENABLED(CONFIG_RISCV_MISALIGNED))
>>>>> + return handle_scalar_misaligned_load(regs);
>>>>> +
>>>>> + return -1;
>>>>> +}
>>>>> +
>>>>> +int handle_misaligned_store(struct pt_regs *regs)
>>>>> +{
>>>>> + if (IS_ENABLED(CONFIG_RISCV_MISALIGNED))
>>>>> + return handle_scalar_misaligned_store(regs);
>>>>> +
>>>>> + return -1;
>>>>> +}
>>>>> +
>>>>> +#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
>>>>> +static void check_vector_unaligned_access_emulated(struct work_struct *unused)
>>>>> +{
>>>>> + long *mas_ptr = this_cpu_ptr(&vector_misaligned_access);
>>>>> + unsigned long tmp_var;
>>>>> +
>>>>> + *mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN;
>>>>> +
>>>>> + local_irq_enable();
>> @Evan Green I forgot to remove this from when when I was using
>> smp_call_on_cpu and encountered the problem you descibed.
>> They can be removed.
>>
>>>>> + kernel_vector_begin();
>>>>> + __asm__ __volatile__ (
>>>>> + ".balign 4\n\t"
>>>>> + ".option push\n\t"
>>>>> + ".option arch, +zve32x\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");
>>>>> + kernel_vector_end();
>> if (*mas_ptr == RISCV_HWPROBE_VEC_MISALIGNED_UNKNOWN)
>> *mas_ptr = RISCV_HWPROBE_VEC_MISALIGNED_SLOW;
>>
>>>>> +}
>>>>> +
>>>>> +bool check_vector_unaligned_access_emulated_all_cpus(void)
>>>
>>> Hopefully I catch the final things I want to say in this email ;)
>>>
>>>>> +{
>>>>> + int cpu;
>>>>> + bool ret = true;
>>>>> +
>>>>> + if (!has_vector()) {
>>>>> + for_each_online_cpu(cpu)
>>>>> + per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>>> + return false;
>>>>> + }
>>>>> +
>>>>> + schedule_on_each_cpu(check_vector_unaligned_access_emulated);
>>>>> +
>>>>> + for_each_online_cpu(cpu)
>>>>> + if (per_cpu(vector_misaligned_access, cpu)
>>>>> + != RISCV_HWPROBE_VEC_MISALIGNED_SLOW)
>>>>> + return false;
>>>
>>> The default value of vector_misaligned_access is
>>> RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED so when the hardware supports
>>> unaligned accesses this will return false. If the hardware doesn't
>>> support unaligned accesses, then the trap will happen and the kernel
>>> will set this variable to UNSUPPORTED, causing this function to again
>>> return false.
>>>
>>> Having the default value be UNKNOWN and checking for UNKNOWN here and in
>>> check_vector_unaligned_access() can remedy this issue.
>>
>> I meant to set it to SLOW in check_vector_unaligned_access_emulated like
>> above.
>
> What "it" are you referring to?

`per_cpu(vector_misaligned_access, cpu)`

> UNKNOWN should be the default internally
> here, not SLOW. Before probing is done, the speed is unknown, so UNKNOWN
> is the logical default.

The scalar hwprobe returns SLOW if misaligned accesses are not emulated.
Rather then storing UNKNOWN in the kernel, I thought it would be better
to set it to slow until we know its fast as it has the same affect as
swaping unknown for slow in sys_hwprobe. The reason i want to keep the
code like this is because if missaligned vector loads work then sudenly
dont we wont ignore them in handle_vector_misaligned_load because the
the instruction should have worked. I can change it to be unknown though
and swap UNKNOWN for SLOW in hwprobe.

Thanks,
Jesse Taube
>
>>
>>> - Charlie
>>>
>>>>> +
>>>>> + return ret;
>>>>> +}
>>>>> +#else
>>>>> +bool check_vector_unaligned_access_emulated_all_cpus(void)
>>>>> +{
>>>>> + return false;
>>>>> +}
>>>>> +#endif
>>>>> +
>>>>> +#ifdef CONFIG_RISCV_MISALIGNED
>>>>> +
>>>>> +static bool unaligned_ctl __read_mostly;
>>>>> +
>>>>> static void check_unaligned_access_emulated(struct work_struct *unused)
>>>>> {
>>>>> int cpu = smp_processor_id();
>>>>> @@ -563,3 +668,9 @@ bool unaligned_ctl_available(void)
>>>>> {
>>>>> return unaligned_ctl;
>>>>> }
>>>>> +#else
>>>>> +bool check_unaligned_access_emulated_all_cpus(void)
>>>>> +{
>>>>> + return false;
>>>>> +}
>>>>> +#endif
>>>>> diff --git a/arch/riscv/kernel/unaligned_access_speed.c b/arch/riscv/kernel/unaligned_access_speed.c
>>>>> index 70c1588fc353..c6106bd4a25a 100644
>>>>> --- a/arch/riscv/kernel/unaligned_access_speed.c
>>>>> +++ b/arch/riscv/kernel/unaligned_access_speed.c
>>>>> @@ -19,7 +19,8 @@
>>>>> #define MISALIGNED_BUFFER_ORDER get_order(MISALIGNED_BUFFER_SIZE)
>>>>> #define MISALIGNED_COPY_SIZE ((MISALIGNED_BUFFER_SIZE / 2) - 0x80)
>>>>> -DEFINE_PER_CPU(long, misaligned_access_speed);
>>>>> +DEFINE_PER_CPU(long, misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_UNKNOWN;
>>>>> +DEFINE_PER_CPU(long, vector_misaligned_access) = RISCV_HWPROBE_VEC_MISALIGNED_UNSUPPORTED;
>>>>> #ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>>>> static cpumask_t fast_misaligned_access;
>>>>> @@ -268,12 +269,18 @@ static int check_unaligned_access_all_cpus(void)
>>>>> if (riscv_has_extension_unlikely(RISCV_ISA_EXT_ZICCLSM)) {
>>>>> for_each_online_cpu(cpu) {
>>>>> +#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
>>>>> + per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VEC_MISALIGNED_FAST;
>>>>> +#endif
>>>>> +#ifdef CONFIG_RISCV_MISALIGNED
>>>>> per_cpu(misaligned_access_speed, cpu) = RISCV_HWPROBE_MISALIGNED_FAST;
>>>>> +#endif
>>>>> }
>>>>> return 0;
>>>>
>>>> Since this function returns 0 in both cases, can you wrap the rest of
>>>> the function with an else and remove this early return?
>>
>> I think its more readable in a guard clause style.
>
> By guard clause style are you referring to how it is right now?

yes.

> It's the
> same return value of 0 in both cases and the most common way of doing
> that is by having a single line for the return at the bottom of the
> function instead of duplicating the return.
>
> - Charlie
>
>>
>>
>> Thanks,
>> Jesse Taube
>>>> - Charlie
>>>>
>>>>> }
>>>>> all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
>>>>> + check_vector_unaligned_access_emulated_all_cpus();
>>>>> #ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
>>>>> if (!all_cpus_emulated)
>>>>> diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c
>>>>> index 682b3feee451..821818886fab 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
>>>>>