From: Clément Léger cleger@rivosinc.com
[ Upstream commit 1317045a7d6f397904d105f6d40dc9787876a34b ]
While misaligned_access_speed was defined in a file compile with CONFIG_RISCV_MISALIGNED, its definition was under CONFIG_RISCV_SCALAR_MISALIGNED. This resulted in compilation problems when using it in a file compiled with CONFIG_RISCV_MISALIGNED.
Move the declaration under CONFIG_RISCV_MISALIGNED so that it can be used unconditionnally when compiled with that config and remove the check for that variable in traps_misaligned.c.
Signed-off-by: Clément Léger cleger@rivosinc.com Reviewed-by: Charlie Jenkins charlie@rivosinc.com Tested-by: Charlie Jenkins charlie@rivosinc.com Reviewed-by: Andrew Jones ajones@ventanamicro.com Link: https://lore.kernel.org/r/20250523101932.1594077-9-cleger@rivosinc.com Signed-off-by: Palmer Dabbelt palmer@dabbelt.com Signed-off-by: Sasha Levin sashal@kernel.org ---
**YES**
This commit should be backported to stable kernel trees.
## Analysis
This commit fixes a **compilation configuration dependency issue** in the RISC-V architecture's misaligned access handling code. Here's my detailed analysis:
### The Problem Fixed The commit addresses a compilation issue where:
1. **Variable Declaration Mismatch**: The `misaligned_access_speed` per- CPU variable was defined in `unaligned_access_speed.c` under `CONFIG_RISCV_MISALIGNED`, but its declaration in `cpufeature.h` was under `CONFIG_RISCV_SCALAR_MISALIGNED`.
2. **Configuration Hierarchy**: From the Kconfig analysis: - `CONFIG_RISCV_MISALIGNED` is a broader umbrella config - `CONFIG_RISCV_SCALAR_MISALIGNED` selects `CONFIG_RISCV_MISALIGNED` - Both `traps_misaligned.c` and `unaligned_access_speed.c` are compiled under `CONFIG_RISCV_MISALIGNED`
3. **Compilation Failure**: When `CONFIG_RISCV_MISALIGNED` is enabled but `CONFIG_RISCV_SCALAR_MISALIGNED` is not, code in `traps_misaligned.c` tries to use `misaligned_access_speed` (line 372: `*this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED;`) but the variable isn't declared in the header.
### The Fix The commit makes two key changes:
1. **In `cpufeature.h`**: Moves the `DECLARE_PER_CPU(long, misaligned_access_speed);` declaration from `CONFIG_RISCV_SCALAR_MISALIGNED` to `CONFIG_RISCV_MISALIGNED` (lines 82-84 in the new version)
2. **In `traps_misaligned.c`**: Removes the conditional `#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS` guard around the assignment to `misaligned_access_speed` (line 372), making it unconditional when compiled under `CONFIG_RISCV_MISALIGNED`
### Why This Should Be Backported
1. **Fixes Compilation Errors**: This is a clear build fix for valid kernel configurations, preventing compilation failures that would break the kernel build.
2. **Small and Contained**: The changes are minimal - just moving a declaration to the correct config section and removing an unnecessary guard.
3. **No Functional Changes**: This doesn't change runtime behavior, only fixes the build system configuration dependencies.
4. **Low Risk**: The fix aligns the declaration with where the variable is actually used, making the code more consistent and correct.
5. **Matches Stable Criteria**: Similar to **Similar Commit #4** which was marked as backport candidate (YES), this fixes compilation issues in configuration management without introducing new features or architectural changes.
6. **Critical Subsystem**: Unaligned access handling is important for RISC-V platforms, and build failures in this area prevent kernel compilation for affected configurations.
This is exactly the type of build fix that stable trees should include - it resolves compilation errors without changing functionality or introducing regression risks.
arch/riscv/include/asm/cpufeature.h | 5 ++++- arch/riscv/kernel/traps_misaligned.c | 2 -- 2 files changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/include/asm/cpufeature.h b/arch/riscv/include/asm/cpufeature.h index f56b409361fbe..7201da46694f7 100644 --- a/arch/riscv/include/asm/cpufeature.h +++ b/arch/riscv/include/asm/cpufeature.h @@ -71,7 +71,6 @@ bool __init check_unaligned_access_emulated_all_cpus(void); void check_unaligned_access_emulated(struct work_struct *work __always_unused); void unaligned_emulation_finish(void); bool unaligned_ctl_available(void); -DECLARE_PER_CPU(long, misaligned_access_speed); #else static inline bool unaligned_ctl_available(void) { @@ -79,6 +78,10 @@ static inline bool unaligned_ctl_available(void) } #endif
+#if defined(CONFIG_RISCV_MISALIGNED) +DECLARE_PER_CPU(long, misaligned_access_speed); +#endif + bool __init check_vector_unaligned_access_emulated_all_cpus(void); #if defined(CONFIG_RISCV_VECTOR_MISALIGNED) void check_vector_unaligned_access_emulated(struct work_struct *work __always_unused); diff --git a/arch/riscv/kernel/traps_misaligned.c b/arch/riscv/kernel/traps_misaligned.c index 77c788660223b..fe0ab912014ba 100644 --- a/arch/riscv/kernel/traps_misaligned.c +++ b/arch/riscv/kernel/traps_misaligned.c @@ -368,9 +368,7 @@ static int handle_scalar_misaligned_load(struct pt_regs *regs)
perf_sw_event(PERF_COUNT_SW_ALIGNMENT_FAULTS, 1, regs, addr);
-#ifdef CONFIG_RISCV_PROBE_UNALIGNED_ACCESS *this_cpu_ptr(&misaligned_access_speed) = RISCV_HWPROBE_MISALIGNED_SCALAR_EMULATED; -#endif
if (!unaligned_enabled) return -1;