riscv: add icache flush for nommu sigreturn trampoline

stable inclusion
from stable-v5.10.178
commit 2a4835b8ede001ce88a34f6f0295f4ece2212174
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8D927

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=2a4835b8ede001ce88a34f6f0295f4ece2212174



--------------------------------

commit 8d736482 upstream.

In a NOMMU kernel, sigreturn trampolines are generated on the user
stack by setup_rt_frame. Currently, these trampolines are not instruction
fenced, thus their visibility to ifetch is not guaranteed.

This patch adds a flush_icache_range in setup_rt_frame to fix this
problem.

Signed-off-by: Mathis Salmen <mathis.salmen@matsal.de>
Fixes: 6bd33e1e ("riscv: add nommu support")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20230406101130.82304-1-mathis.salmen@matsal.de


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>