From 2843ade2dad2249900f508f61068d245921ce9f1 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 14 Nov 2017 14:33:28 +0000 Subject: [PATCH] arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks Commit 18011eac28c7 upstream. 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 Signed-off-by: Ard Biesheuvel Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/process.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index bcd22d7..9e77373 100644 --- a/arch/arm64/kernel/process.c +++ b/arch/arm64/kernel/process.c @@ -314,16 +314,14 @@ 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 */ -- 2.7.4