diff mbox series

[v2,15/18] arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks

Message ID 1512059986-21325-16-git-send-email-will.deacon@arm.com
State Superseded
Headers show
Series arm64: Unmap the kernel whilst running in userspace (KAISER) | expand

Commit Message

Will Deacon Nov. 30, 2017, 4:39 p.m. UTC 
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.

Signed-off-by: Will Deacon <will.deacon@arm.com>

---
 arch/arm64/kernel/process.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

-- 
2.1.4
diff mbox series

Patch

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index b2adcce7bc18..aba3a1fb492d 100644
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -361,16 +361,14 @@  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 */