[PATCH 13/29] arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks

[Alex Shi]

From: Will Deacon <will.deacon at arm.com>

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 <mark.rutland at arm.com>
Tested-by: Laura Abbott <labbott at redhat.com>
Tested-by: Shanker Donthineni <shankerd at codeaurora.org>
Signed-off-by: Will Deacon <will.deacon at arm.com>
Signed-off-by: Alex Shi <alex.shi at linaro.org>

Conflicts:
	fold tls_preserve_current_state() in arch/arm64/kernel/process.c
---
 arch/arm64/kernel/process.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 0e73949..0972ce5 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -306,17 +306,17 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,
 
 static void tls_thread_switch(struct task_struct *next)
 {
-	unsigned long tpidr, tpidrro;
+	unsigned long tpidr;
 
 	tpidr = read_sysreg(tpidr_el0);
 	*task_user_tls(current) = tpidr;
 
-	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