riscv: Decouple emulated unaligned accesses from access speed

Detecting if a system traps into the kernel on an unaligned access
can be performed separately from checking the speed of unaligned
accesses. This decoupling will make it possible to selectively enable
or disable each of these checks.

Signed-off-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>
Link: https://lore.kernel.org/r/20240308-disable_misaligned_probe_config-v9-3-a388770ba0ce@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 466e1f591919bf9a4e320ee08ccadb31201897a4..6fec91845aa099f30bf97098761211f42f91cf61 100644 (file)
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -37,7 +37,7 @@ void riscv_user_isa_enable(void);
 
 #ifdef CONFIG_RISCV_MISALIGNED
 bool unaligned_ctl_available(void);
-bool check_unaligned_access_emulated(int cpu);
+bool check_unaligned_access_emulated_all_cpus(void);
 void unaligned_emulation_finish(void);
 #else
 static inline bool unaligned_ctl_available(void)

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 7878cddccc0de1c052c82f5e60f865481f39a511..abb3a2f531061d04f5efa50c74ed791cef7b44ac 100644 (file)
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -719,7 +719,8 @@ static int check_unaligned_access(void *param)
        void *src;
        long speed = RISCV_HWPROBE_MISALIGNED_SLOW;
 
-       if (check_unaligned_access_emulated(cpu))
+       if (IS_ENABLED(CONFIG_RISCV_MISALIGNED) &&
+           per_cpu(misaligned_access_speed, cpu) != RISCV_HWPROBE_MISALIGNED_UNKNOWN)
                return 0;
 
        /* Make an unaligned destination buffer. */
@@ -896,8 +897,8 @@ static int riscv_offline_cpu(unsigned int cpu)
        return 0;
 }
 
-/* Measure unaligned access on all CPUs present at boot in parallel. */
-static int check_unaligned_access_all_cpus(void)
+/* Measure unaligned access speed on all CPUs present at boot in parallel. */
+static int check_unaligned_access_speed_all_cpus(void)
 {
        unsigned int cpu;
        unsigned int cpu_count = num_possible_cpus();
@@ -935,7 +936,6 @@ static int check_unaligned_access_all_cpus(void)
                                  riscv_online_cpu, riscv_offline_cpu);
 
 out:
-       unaligned_emulation_finish();
        for_each_cpu(cpu, cpu_online_mask) {
                if (bufs[cpu])
                        __free_pages(bufs[cpu], MISALIGNED_BUFFER_ORDER);
@@ -945,6 +945,23 @@ out:
        return 0;
 }
 
+#ifdef CONFIG_RISCV_MISALIGNED
+static int check_unaligned_access_all_cpus(void)
+{
+       bool all_cpus_emulated = check_unaligned_access_emulated_all_cpus();
+
+       if (!all_cpus_emulated)
+               return check_unaligned_access_speed_all_cpus();
+
+       return 0;
+}
+#else
+static int check_unaligned_access_all_cpus(void)
+{
+       return check_unaligned_access_speed_all_cpus();
+}
+#endif
+
 arch_initcall(check_unaligned_access_all_cpus);
 
 void riscv_user_isa_enable(void)

diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index c2ed4e689bf96d5d31a081ce4ab04483599dac8f..e55718179f4284f4a8bc8f6cb73d782ea9f96d8f 100644 (file)
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -596,7 +596,7 @@ int handle_misaligned_store(struct pt_regs *regs)
        return 0;
 }
 
-bool check_unaligned_access_emulated(int cpu)
+static bool check_unaligned_access_emulated(int cpu)
 {
        long *mas_ptr = per_cpu_ptr(&misaligned_access_speed, cpu);
        unsigned long tmp_var, tmp_val;
@@ -623,7 +623,7 @@ bool check_unaligned_access_emulated(int cpu)
        return misaligned_emu_detected;
 }
 
-void unaligned_emulation_finish(void)
+bool check_unaligned_access_emulated_all_cpus(void)
 {
        int cpu;
 
@@ -632,13 +632,12 @@ void unaligned_emulation_finish(void)
         * accesses emulated since tasks requesting such control can run on any
         * CPU.
         */
-       for_each_online_cpu(cpu) {
-               if (per_cpu(misaligned_access_speed, cpu) !=
-                                       RISCV_HWPROBE_MISALIGNED_EMULATED) {
-                       return;
-               }
-       }
+       for_each_online_cpu(cpu)
+               if (!check_unaligned_access_emulated(cpu))
+                       return false;
+
        unaligned_ctl = true;
+       return true;
 }
 
 bool unaligned_ctl_available(void)