From 59eae0dbcf6c0cfb428f2bfb167af8a281026a05 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Tue, 14 Nov 2017 14:33:28 +0000 Subject: [PATCH] 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 Tested-by: Laura Abbott Tested-by: Shanker Donthineni Signed-off-by: Will Deacon (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 Signed-off-by: Greg Kroah-Hartman --- arch/arm64/kernel/process.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) diff --git a/arch/arm64/kernel/process.c b/arch/arm64/kernel/process.c index 5ac462f222f8..dfbabc0e274b 100644 --- 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 */ -- 2.20.1