From: Will Deacon Date: Tue, 14 Nov 2017 14:33:28 +0000 (+0000) Subject: arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks X-Git-Url: http://git.cdn.openwrt.org/?a=commitdiff_plain;h=18011eac28c7cb31c87b86b7d0e5b01894405c7f;p=openwrt%2Fstaging%2Fblogic.git arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks When unmapping the kernel at EL0, we use tpidrro_el0 as a scratch register during exception entry from native tasks and subsequently zero it in the kernel_ventry macro. We can therefore avoid zeroing tpidrro_el0 in the context-switch path for native tasks using the entry trampoline. Reviewed-by: Mark Rutland Tested-by: Laura Abbott Tested-by: Shanker Donthineni Signed-off-by: Will Deacon --- diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 6b7dcf4310ac..583fd8154695 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -370,16 +370,14 @@ void tls_preserve_current_state(void) static void tls_thread_switch(struct task_struct *next) { - unsigned long tpidr, tpidrro; - tls_preserve_current_state(); - tpidr = *task_user_tls(next); - tpidrro = is_compat_thread(task_thread_info(next)) ? - next->thread.tp_value : 0; + if (is_compat_thread(task_thread_info(next))) + write_sysreg(next->thread.tp_value, tpidrro_el0); + else if (!arm64_kernel_unmapped_at_el0()) + write_sysreg(0, tpidrro_el0); - write_sysreg(tpidr, tpidr_el0); - write_sysreg(tpidrro, tpidrro_el0); + write_sysreg(*task_user_tls(next), tpidr_el0); } /* Restore the UAO state depending on next's addr_limit */