[PATCH 1/2] arm64: entry: remove pointless SPSR mode check

Mark Rutland
2016-01-05T17:33:34Z

In work_pending we may skip work if the stacked SPSR value represents
anything other than an EL0 context. We then immediately invoke the
kernel_exit 0 macro as part of ret_to_user, assuming a return to EL0.
This is somewhat confusing.

We use work_pending as part of the ret_to_user/ret_fast_syscall state
machine. We only use ret_fast_syscall in the return from an SVC issued
from EL0. We use ret_to_user for return from EL0 exception handlers and
also for return from ret_from_fork in the case the task was not a kernel
thread (i.e. it is a user task).

Thus in all cases the stacked SPSR value must represent an EL0 context,
and the check is redundant. This patch removes it, along with the now
unused no_work_pending label.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chris Metcalf <cmetcalf@ezchip.com>
Cc: Will Deacon <will.deacon@arm.com>
---
arch/arm64/kernel/entry.S | 4 ----
1 file changed, 4 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index 7ed3d75..6b30ab1 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -626,10 +626,7 @@ ret_fast_syscall_trace:
work_pending:
tbnz x1, #TIF_NEED_RESCHED, work_resched
/* TIF_SIGPENDING, TIF_NOTIFY_RESUME or TIF_FOREIGN_FPSTATE case */
- ldr x2, [sp, #S_PSTATE]
mov x0, sp // 'regs'
- tst x2, #PSR_MODE_MASK // user mode regs?
- b.ne no_work_pending // returning to kernel
enable_irq // enable interrupts for do_notify_resume()
bl do_notify_resume
b ret_to_user
@@ -645,7 +642,6 @@ ret_to_user:
and x2, x1, #_TIF_WORK_MASK
cbnz x2, work_pending
enable_step_tsk x1, x2
-no_work_pending:
kernel_exit 0
ENDPROC(ret_to_user)

--
1.9.1