linux-kernel - [PATCH 2/2] riscv: Disable misaligned access probe when CONFIG_HAVE_EFFICIENT_UNALIGNED

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Message-Id: <20240131-disable_misaligned_probe_config-v1-2-98d155e9cda8@rivosinc.com>
Date: Wed, 31 Jan 2024 22:40:23 -0800
From: Charlie Jenkins <charlie@...osinc.com>
To: Paul Walmsley <paul.walmsley@...ive.com>, 
 Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, 
 Jisheng Zhang <jszhang@...nel.org>, Evan Green <evan@...osinc.com>
Cc: linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Charlie Jenkins <charlie@...osinc.com>
Subject: [PATCH 2/2] riscv: Disable misaligned access probe when
 CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS

When CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS is selected, the cpus can be
set to have fast misaligned access without needing to probe.

Signed-off-by: Charlie Jenkins <charlie@...osinc.com>
---
 arch/riscv/include/asm/cpufeature.h  | 7 +++++++
 arch/riscv/kernel/cpufeature.c       | 4 ++++
 arch/riscv/kernel/sys_hwprobe.c      | 4 ++++
 arch/riscv/kernel/traps_misaligned.c | 4 ++++
 4 files changed, 19 insertions(+)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index dfdcca229174..7d8d64783e38 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -137,10 +137,17 @@ static __always_inline bool riscv_cpu_has_extension_unlikely(int cpu, const unsi
 	return __riscv_isa_extension_available(hart_isa[cpu].isa, ext);
 }
 
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 DECLARE_STATIC_KEY_FALSE(fast_misaligned_access_speed_key);
 
 static __always_inline bool has_fast_misaligned_accesses(void)
 {
 	return static_branch_likely(&fast_misaligned_access_speed_key);
 }
+#else
+static __always_inline bool has_fast_misaligned_accesses(void)
+{
+	return true;
+}
+#endif
 #endif
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 89920f84d0a3..d787846c0b68 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -43,10 +43,12 @@ static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 /* Per-cpu ISA extensions. */
 struct riscv_isainfo hart_isa[NR_CPUS];
 
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 /* Performance information */
 DEFINE_PER_CPU(long, misaligned_access_speed);
 
 static cpumask_t fast_misaligned_access;
+#endif
 
 /**
  * riscv_isa_extension_base() - Get base extension word
@@ -706,6 +708,7 @@ unsigned long riscv_get_elf_hwcap(void)
 	return hwcap;
 }
 
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 static int check_unaligned_access(void *param)
 {
 	int cpu = smp_processor_id();
@@ -946,6 +949,7 @@ static int check_unaligned_access_all_cpus(void)
 }
 
 arch_initcall(check_unaligned_access_all_cpus);
+#endif /* CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS */
 
 void riscv_user_isa_enable(void)
 {
diff --git a/arch/riscv/kernel/sys_hwprobe.c b/arch/riscv/kernel/sys_hwprobe.c
index a7c56b41efd2..3f1a6edfdb08 100644
--- a/arch/riscv/kernel/sys_hwprobe.c
+++ b/arch/riscv/kernel/sys_hwprobe.c
@@ -149,6 +149,7 @@ static bool hwprobe_ext0_has(const struct cpumask *cpus, unsigned long ext)
 
 static u64 hwprobe_misaligned(const struct cpumask *cpus)
 {
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	int cpu;
 	u64 perf = -1ULL;
 
@@ -168,6 +169,9 @@ static u64 hwprobe_misaligned(const struct cpumask *cpus)
 		return RISCV_HWPROBE_MISALIGNED_UNKNOWN;
 
 	return perf;
+#else
+	return RISCV_HWPROBE_MISALIGNED_FAST;
+#endif
 }
 
 static void hwprobe_one_pair(struct riscv_hwprobe *pair,
diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index 8ded225e8c5b..c24f79d769f6 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -413,7 +413,9 @@ int handle_misaligned_load(struct pt_regs *regs)
 
 	perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
 
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 	*this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_EMULATED;
+#endif
 
 	if (!unaligned_enabled)
 		return -1;
@@ -596,6 +598,7 @@ int handle_misaligned_store(struct pt_regs *regs)
 	return 0;
 }
 
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
 bool check_unaligned_access_emulated(int cpu)
 {
 	long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
@@ -640,6 +643,7 @@ void unaligned_emulation_finish(void)
 	}
 	unaligned_ctl = true;
 }
+#endif
 
 bool unaligned_ctl_available(void)
 {

-- 
2.43.0