[PATCH v4 5/7] RISC-V: Detect unaligned vector accesses supported

From: Jesse Taube
Date: Thu Jul 11 2024 - 18:00:39 EST

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@xxxxxxxxxxxx>
---
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
---
arch/riscv/Kconfig | 35 ++++++
arch/riscv/include/asm/cpufeature.h | 5 +
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 | 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, 213 insertions(+), 29 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 0ed7d99c14dd..f25f56f9bfaa 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -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 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..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..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 1a1bb41472ea..42eeabfa3d95 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
+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_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;
+}
+
+bool check_vector_unaligned_access_emulated_all_cpus(void)
+{
+ int cpu;
+
+ if (!has_vector()) {
+ for_each_online_cpu(cpu)
+ per_cpu(vector_misaligned_access, cpu) = RISCV_HWPROBE_VECTOR_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_VECTOR_MISALIGNED_SLOW)
+ return false;
+
+ return true;
+}
+#else
+bool check_vector_unaligned_access_emulated_all_cpus(void)
+{
+ return false;
+}
+#endif
+
+#ifdef CONFIG_RISCV_SCALAR_MISALIGNED
+
+static bool unaligned_ctl __read_mostly;
+
static void check_unaligned_access_emulated(struct work_struct *unused)
{
int cpu = smp_processor_id();
@@ -574,3 +680,9 @@ 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 a9a6bcb02acf..24b8883a23f0 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_VECTOR_MISALIGNED_UNSUPPORTED;

#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS
static cpumask_t fast_misaligned_access;
@@ -259,23 +260,24 @@ static int check_unaligned_access_speed_all_cpus(void)
kfree(bufs);
return 0;
}
+#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
+static int check_unaligned_access_speed_all_cpus(void)
+{
+ return 0;
+}
+#endif

static int check_unaligned_access_all_cpus(void)
{
- bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
+ bool all_cpus_emulated;
+
+ all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
+ check_vector_unaligned_access_emulated_all_cpus();

if (!all_cpus_emulated)
return check_unaligned_access_speed_all_cpus();

return 0;
}
-#else /* CONFIG_RISCV_PROBE_UNALIGNED_ACCESS */
-static int check_unaligned_access_all_cpus(void)
-{
- check_unaligned_access_emulated_all_cpus();
-
- return 0;
-}
-#endif

arch_initcall(check_unaligned_access_all_cpus);
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;
--
2.45.2