FROMLIST: 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 <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git
 commit 18011eac28c7cb31c87b86b7d0e5b01894405c7f)

Change-Id: Ief7b4099f055420a7a23c8dcf497269192f5fb58
[ghackmann@google.com: adjust context]
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c
index 5ac462f..dfbabc0 100644 (file)
--- a/arch/arm64/kernel/process.c
+++ b/arch/arm64/kernel/process.c
@@ -376,19 +376,17 @@ 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;
 
        asm("mrs %0, tpidr_el0" : "=r" (tpidr));
        *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);
 
-       asm(
-       "       msr     tpidr_el0, %0\n"
-       "       msr     tpidrro_el0, %1"
-       : : "r" (tpidr), "r" (tpidrro));
+       write_sysreg(*task_user_tls(next), tpidr_el0);
 }
 
 /* Restore the UAO state depending on next's addr_limit */