From: Will Deacon will@kernel.org
commit fca3d33d8ad61eb53eca3ee4cac476d1e31b9008 upstream.
When all CPUs in the system implement the SSBS extension, the SSBS field in PSTATE is the definitive indication of the mitigation state. Further, when the CPUs implement the SSBS manipulation instructions (advertised to userspace via an HWCAP), EL0 can toggle the SSBS field directly and so we cannot rely on any shadow state such as TIF_SSBD at all.
Avoid forcing the SSBS field in context-switch on such a system, and simply rely on the PSTATE register instead.
Cc: stable@vger.kernel.org Cc: Catalin Marinas catalin.marinas@arm.com Cc: Srinivas Ramana sramana@codeaurora.org Fixes: cbdf8a189a66 ("arm64: Force SSBS on context switch") Reviewed-by: Marc Zyngier maz@kernel.org Signed-off-by: Will Deacon will@kernel.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/arm64/kernel/process.c | 7 +++++++ 1 file changed, 7 insertions(+)
--- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -354,6 +354,13 @@ static void ssbs_thread_switch(struct ta if (unlikely(next->flags & PF_KTHREAD)) return;
+ /* + * If all CPUs implement the SSBS extension, then we just need to + * context-switch the PSTATE field. + */ + if (cpu_have_feature(cpu_feature(SSBS))) + return; + /* If the mitigation is enabled, then we leave SSBS clear. */ if ((arm64_get_ssbd_state() == ARM64_SSBD_FORCE_ENABLE) || test_tsk_thread_flag(next, TIF_SSBD))