Commit f47c91dc authored Nov 14, 2017 by Will Deacon Committed by Greg Kroah-Hartman Jan 05, 2018

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
 - replace task_user_tls() accessor with equivalent field from 3.18]
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

parent 1766a613

arch/arm64/kernel/process.c

+6 −13

Original line number	Diff line number	Diff line
		@@ -362,25 +362,18 @@ int copy_thread(unsigned long clone_flags, unsigned long stack_start,

		static void tls_thread_switch(struct task_struct *next)
		{
		unsigned long tpidr, tpidrro;

		if (!is_compat_task()) {
		unsigned long tpidr;
		asm("mrs %0, tpidr_el0" : "=r" (tpidr));
		current->thread.tp_value = tpidr;
		}

		if (is_compat_thread(task_thread_info(next))) {
		tpidr = 0;
		tpidrro = next->thread.tp_value;
		} else {
		tpidr = next->thread.tp_value;
		tpidrro = 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(next->thread.tp_value, tpidr_el0);
		}

		/* Restore the UAO state depending on next's addr_limit */