[PATCH v3 08/17] riscv: misaligned: add a function to check misalign trap delegability

Clément Léger
2025-03-10T15:13:54Z

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>
---
arch/riscv/include/asm/cpufeature.h | 5 +++++
arch/riscv/kernel/traps_misaligned.c | 17 +++++++++++++++--
2 files changed, 20 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h
index ad7d26788e6a..8b97cba99fc3 100644
--- a/arch/riscv/include/asm/cpufeature.h
+++ b/arch/riscv/include/asm/cpufeature.h
@@ -69,12 +69,17 @@ int cpu_online_unaligned_access_init(unsigned int cpu);
#if defined(CONFIG_RISCV_SCALAR_MISALIGNED)
void unaligned_emulation_finish(void);
bool unaligned_ctl_available(void);
+bool misaligned_traps_can_delegate(void);
DECLARE_PER_CPU(long, misaligned_access_speed);
#else
static inline bool unaligned_ctl_available(void)
{
return false;
}
+static inline bool misaligned_traps_can_delegate(void)
+{
+ return false;
+}
#endif

bool 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 db31966a834e..a67a6e709a06 100644
--- a/arch/riscv/kernel/traps_misaligned.c
+++ b/arch/riscv/kernel/traps_misaligned.c
@@ -716,10 +716,10 @@ 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) &&
@@ -761,6 +761,7 @@ static int cpu_online_sbi_unaligned_setup(unsigned int cpu __always_unused)
{
return 0;
}
+
#endif

int cpu_online_unaligned_access_init(unsigned int cpu)
@@ -773,3 +774,15 @@ 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 implemented 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);
\ No newline at end of file
--
2.47.2