From: Andy Chiu andy.chiu@sifive.com
commit 8547649981e6631328cd64f583667501ae385531 upstream.
In RISCV, we must use an AUIPC + JALR pair to encode an immediate, forming a jump that jumps to an address over 4K. This may cause errors if we want to enable kernel preemption and remove dependency from patching code with stop_machine(). For example, if a task was switched out on auipc. And, if we changed the ftrace function before it was switched back, then it would jump to an address that has updated 11:0 bits mixing with previous XLEN:12 part.
p: patched area performed by dynamic ftrace ftrace_prologue: p| REG_S ra, -SZREG(sp) p| auipc ra, 0x? ------------> preempted ... change ftrace function ... p| jalr -?(ra) <------------- switched back p| REG_L ra, -SZREG(sp) func: xxx ret
Fixes: afc76b8b8011 ("riscv: Using PATCHABLE_FUNCTION_ENTRY instead of MCOUNT") Signed-off-by: Andy Chiu andy.chiu@sifive.com Signed-off-by: Guo Ren guoren@kernel.org Link: https://lore.kernel.org/r/20230112090603.1295340-2-guoren@kernel.org Cc: stable@vger.kernel.org Signed-off-by: Palmer Dabbelt palmer@rivosinc.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/riscv/Kconfig | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/arch/riscv/Kconfig +++ b/arch/riscv/Kconfig @@ -138,7 +138,7 @@ config RISCV select HAVE_DYNAMIC_FTRACE_WITH_REGS if HAVE_DYNAMIC_FTRACE select HAVE_FTRACE_MCOUNT_RECORD if !XIP_KERNEL select HAVE_FUNCTION_GRAPH_TRACER - select HAVE_FUNCTION_TRACER if !XIP_KERNEL + select HAVE_FUNCTION_TRACER if !XIP_KERNEL && !PREEMPTION
config ARCH_MMAP_RND_BITS_MIN default 18 if 64BIT