linux-kernel - [PATCH v4 10/26] arm64: Delay daif masking for user return

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Date:   Fri, 25 May 2018 10:49:16 +0100
From:   Julien Thierry <julien.thierry@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, daniel.thompson@...aro.org,
        joel@...lfernandes.org, marc.zyngier@....com, mark.rutland@....com,
        christoffer.dall@....com, james.morse@....com,
        catalin.marinas@....com, will.deacon@....com,
        Julien Thierry <julien.thierry@....com>
Subject: [PATCH v4 10/26] arm64: Delay daif masking for user return

Masking daif flags is done very early before returning to EL0.

Only toggle the interrupt masking while in the vector entry and mask daif
once in kernel_exit.

Signed-off-by: Julien Thierry <julien.thierry@....com>
Cc: Catalin Marinas <catalin.marinas@....com>
Cc: Will Deacon <will.deacon@....com>
Cc: Mark Rutland <mark.rutland@....com>
Cc: James Morse <james.morse@....com>
---
 arch/arm64/kernel/entry.S | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/kernel/entry.S b/arch/arm64/kernel/entry.S
index ec2ee72..20252d5 100644
--- a/arch/arm64/kernel/entry.S
+++ b/arch/arm64/kernel/entry.S
@@ -240,9 +240,9 @@ alternative_else_nop_endif
 	.endm
 
 	.macro	kernel_exit, el
-	.if	\el != 0
 	disable_daif
 
+	.if	\el != 0
 	/* Restore the task's original addr_limit. */
 	ldr	x20, [sp, #S_ORIG_ADDR_LIMIT]
 	str	x20, [tsk, #TSK_TI_ADDR_LIMIT]
@@ -872,7 +872,7 @@ ENDPROC(el0_error)
  * and this includes saving x0 back into the kernel stack.
  */
 ret_fast_syscall:
-	disable_daif
+	disable_irq				// disable interrupts
 	str	x0, [sp, #S_X0]			// returned x0
 	ldr	x1, [tsk, #TSK_TI_FLAGS]	// re-check for syscall tracing
 	and	x2, x1, #_TIF_SYSCALL_WORK
@@ -882,7 +882,7 @@ ret_fast_syscall:
 	enable_step_tsk x1, x2
 	kernel_exit 0
 ret_fast_syscall_trace:
-	enable_daif
+	enable_irq				// enable interrupts
 	b	__sys_trace_return_skipped	// we already saved x0
 
 /*
@@ -900,7 +900,7 @@ work_pending:
  * "slow" syscall return path.
  */
 ret_to_user:
-	disable_daif
+	disable_irq				// disable interrupts
 	ldr	x1, [tsk, #TSK_TI_FLAGS]
 	and	x2, x1, #_TIF_WORK_MASK
 	cbnz	x2, work_pending
-- 
1.9.1