[PATCH v6 6/8] RISC-V: Detect unaligned vector accesses supported
Evan Green
evan at rivosinc.com
Thu Jul 25 11:59:07 PDT 2024
On Wed, Jul 24, 2024 at 11:36 AM Jesse Taube <jesse at rivosinc.com> 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 at rivosinc.com>
> Reviewed-by: Charlie Jenkins <charlie at 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
> V2 -> V3:
> - Fixed CONFIG_ in Kconfig
> - Fixed check_vector_unaligned_access_emulated leaving
> vector_misaligned_access as unknown.
> - Remove local_irq_enable
> - Remove RISCV_DETECT_VECTOR_UNALIGNED_ACCESS
> - Remove RISCV_VEC_UNALIGNED_ACCESS_UNSUPPORTED
> V3 -> V4:
> - Spell out _VECTOR_ in macros
> V4 -> V5:
> - Change work_struct *unused to work_struct *work __always_unused
> - Add insn_is_vector definition to vector.h when V is not defined
> V5 -> V6:
> - Change check_vector_unaligned_access_emulated to extern
> - Move check_unaligned_access_emulated_all_cpus out of the #ifdef
> see last commit
> ---
> arch/riscv/Kconfig | 35 ++++++
> arch/riscv/include/asm/cpufeature.h | 8 +-
> arch/riscv/include/asm/entry-common.h | 11 --
> arch/riscv/include/asm/hwprobe.h | 2 +-
> arch/riscv/include/asm/vector.h | 2 +
> arch/riscv/include/uapi/asm/hwprobe.h | 5 +
> arch/riscv/kernel/Makefile | 4 +-
> arch/riscv/kernel/sys_hwprobe.c | 35 ++++++
> arch/riscv/kernel/traps_misaligned.c | 120 ++++++++++++++++++++-
> arch/riscv/kernel/unaligned_access_speed.c | 22 ++--
> arch/riscv/kernel/vector.c | 2 +-
> 11 files changed, 216 insertions(+), 30 deletions(-)
>
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 34d24242e37a..ffbe0fdd7fb3 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -717,12 +717,26 @@ config THREAD_SIZE_ORDER
> Specify the Pages of thread stack size (from 4KB to 64KB), which also
> affects irq stack size, which is equal to thread stack size.
>
> +config RISCV_MISALIGNED
> + bool
> + help
> + Embed support for detecting and emulating misaligned
> + scalar or vector loads and stores.
> +
> config RISCV_SCALAR_MISALIGNED
> bool
> + select RISCV_MISALIGNED
> select SYSCTL_ARCH_UNALIGN_ALLOW
> help
> Embed support for emulating misaligned loads and stores.
>
> +config RISCV_VECTOR_MISALIGNED
> + bool
> + select RISCV_MISALIGNED
> + 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 +788,27 @@ 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_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.
> +
> +endchoice
> +
> endmenu # "Platform type"
>
> menu "Kernel features"
> diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
> index 4ade9f87fc55..5634f702f3fe 100644
> --- a/arch/riscv/include/asm/cpufeature.h
> +++ b/arch/riscv/include/asm/cpufeature.h
> @@ -34,8 +34,8 @@ extern struct riscv_isainfo hart_isa[NR_CPUS];
>
> void riscv_user_isa_enable(void);
>
> -#if defined(CONFIG_RISCV_SCALAR_MISALIGNED)
> bool check_unaligned_access_emulated_all_cpus(void);
> +#if defined(CONFIG_RISCV_SCALAR_MISALIGNED)
> void check_unaligned_access_emulated(struct work_struct *work __always_unused);
> void unaligned_emulation_finish(void);
> bool unaligned_ctl_available(void);
> @@ -47,6 +47,12 @@ static inline bool unaligned_ctl_available(void)
> }
> #endif
>
> +bool check_vector_unaligned_access_emulated_all_cpus(void);
> +#if defined(CONFIG_RISCV_VECTOR_MISALIGNED)
> +void check_vector_unaligned_access_emulated(struct work_struct *work __always_unused);
> +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 0a4e3544c877..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_SCALAR_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..c7c023afbacd 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);
> @@ -268,6 +269,7 @@ struct pt_regs;
>
> static inline int riscv_v_setup_vsize(void) { return -EOPNOTSUPP; }
> static __always_inline bool has_vector(void) { return false; }
> +static __always_inline bool insn_is_vector(u32 insn_buf) { return false; }
> static inline bool riscv_v_first_use_handler(struct pt_regs *regs) { return false; }
> static inline bool riscv_v_vstate_query(struct pt_regs *regs) { return false; }
> static inline bool riscv_v_vstate_ctrl_user_allowed(void) { return false; }
> diff --git a/arch/riscv/include/uapi/asm/hwprobe.h b/arch/riscv/include/uapi/asm/hwprobe.h
> index 023b7771d1b7..48b92fb07edf 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_VECTOR_MISALIGNED_PERF 8
> +#define RISCV_HWPROBE_VECTOR_MISALIGNED_UNKNOWN 0
> +#define RISCV_HWPROBE_VECTOR_MISALIGNED_SLOW 2
> +#define RISCV_HWPROBE_VECTOR_MISALIGNED_FAST 3
> +#define RISCV_HWPROBE_VECTOR_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 8d4e7d40e42f..5b243d46f4b1 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_SCALAR_MISALIGNED) += traps_misaligned.o
> -obj-$(CONFIG_RISCV_SCALAR_MISALIGNED) += unaligned_access_speed.o
> +obj-$(CONFIG_RISCV_MISALIGNED) += traps_misaligned.o
> +obj-$(CONFIG_RISCV_MISALIGNED) += unaligned_access_speed.o
> obj-$(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..2e3e324bad38 100644
> --- a/arch/riscv/kernel/sys_hwprobe.c
> +++ b/arch/riscv/kernel/sys_hwprobe.c
> @@ -194,6 +194,37 @@ 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;
> +
> + /* 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_VECTOR_MISALIGNED_UNKNOWN;
> + break;
> + }
> + }
> +
> + if (perf == -1ULL)
> + return RISCV_HWPROBE_VECTOR_MISALIGNED_UNKNOWN;
> +
> + return perf;
> +}
> +#else
> +static u64 hwprobe_vec_misaligned(const struct cpumask *cpus)
> +{
> + return RISCV_HWPROBE_VECTOR_MISALIGNED_UNKNOWN;
> +}
> +#endif
> +
> static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> const struct cpumask *cpus)
> {
> @@ -222,6 +253,10 @@ static void hwprobe_one_pair(struct riscv_hwprobe *pair,
> pair->value = hwprobe_misaligned(cpus);
> break;
>
> + case RISCV_HWPROBE_KEY_VECTOR_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 bb09357778c5..817496a6a2d5 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_VECTOR_MISALIGNED_UNKNOWN) {
> + *this_cpu_ptr(&vector_misaligned_access) = RISCV_HWPROBE_VECTOR_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 +552,86 @@ 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_SCALAR_MISALIGNED))
> + return handle_scalar_misaligned_load(regs);
> +
> + return -1;
> +}
> +
> +int handle_misaligned_store(struct pt_regs *regs)
> +{
> + if (IS_ENABLED(CONFIG_RISCV_SCALAR_MISALIGNED))
> + return handle_scalar_misaligned_store(regs);
> +
> + return -1;
> +}
> +
> +#ifdef CONFIG_RISCV_VECTOR_MISALIGNED
> +void check_vector_unaligned_access_emulated(struct work_struct *work __always_unused)
> +{
> + long *mas_ptr = this_cpu_ptr(&vector_misaligned_access);
> + unsigned long tmp_var;
> +
> + *mas_ptr = RISCV_HWPROBE_VECTOR_MISALIGNED_UNKNOWN;
> +
> + 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_VECTOR_MISALIGNED_UNKNOWN)
> + *mas_ptr = RISCV_HWPROBE_VECTOR_MISALIGNED_SLOW;
I'm still not a fan of this "if we don't know, say it's slow" thing.
Most consumers of this key will do something like "if
(misaligned_access == FAST) install_fast_functions()", and that'll
work here too. But for usermode that really cares and is trying to
interpret the other values, they're now forced to treat SLOW and
UNKNOWN as the same value, since we sometimes return SLOW when we mean
UNKNOWN. It seems better to me if the kernel is honestly reporting the
information, and then usermode can extract real meaning from each of
these values to the extent they care to.
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