From: Andy Chiu <andy.chiu@xxxxxxxxxx>
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@xxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20230112090603.1295340-2-guoren@xxxxxxxxxx
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
