riscv: misaligned: add a function to check misalign trap delegability

Checking for the delegability of the misaligned access trap is needed
for the KVM FWFT extension implementation. Add a function to get the
delegability of the misaligned trap exception.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20250523101932.1594077-11-cleger@rivosinc.com
Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>

2 files changed, 21 insertions, 2 deletions

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index 2bfa4ef383ed..fbd0e4306c93 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -81,6 +81,12 @@ static inline bool unaligned_ctl_available(void)
 
 #if defined(CONFIG_RISCV_MISALIGNED)
 DECLARE_PER_CPU(long, misaligned_access_speed);
+bool misaligned_traps_can_delegate(void);
+#else
+static inline bool misaligned_traps_can_delegate(void)
+{
+	return false;
+}
 #endif
 
 bool __init check_vector_unaligned_access_emulated_all_cpus(void);
diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c
index 7ecaa8103fe7..93043924fe6c 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -724,10 +724,10 @@ static int cpu_online_check_unaligned_access_emulated(unsigned int cpu)
 }
 #endif
 
-#ifdef CONFIG_RISCV_SBI
-
 static bool misaligned_traps_delegated;
 
+#ifdef CONFIG_RISCV_SBI
+
 static int cpu_online_sbi_unaligned_setup(unsigned int cpu)
 {
 	if (sbi_fwft_set(SBI_FWFT_MISALIGNED_EXC_DELEG, 1, 0) &&
@@ -763,6 +763,7 @@ static int cpu_online_sbi_unaligned_setup(unsigned int cpu __always_unused)
 {
 	return 0;
 }
+
 #endif
 
 int cpu_online_unaligned_access_init(unsigned int cpu)
@@ -775,3 +776,15 @@ int cpu_online_unaligned_access_init(unsigned int cpu)
 
 	return cpu_online_check_unaligned_access_emulated(cpu);
 }
+
+bool misaligned_traps_can_delegate(void)
+{
+	/*
+	 * Either we successfully requested misaligned traps delegation for all
+	 * CPUs, or the SBI does not implement the FWFT extension but delegated
+	 * the exception by default.
+	 */
+	return misaligned_traps_delegated ||
+	       all_cpus_unaligned_scalar_access_emulated();
+}
+EXPORT_SYMBOL_GPL(misaligned_traps_can_delegate);