[RFC PATCH 04/36] arm64: suspend: rely on daif helpers to handle PMR

[Vladimir Murzin]

From: Ada Couprie Diaz <ada.coupriediaz at arm.com>

Commit 77345ef70445 ("arm64: suspend: Use cpuidle context helpers
in cpu_suspend()") added cpuidle helpers to handle PMR manipulation
and restoration to ensure that the CPU receives interrupts when suspended
and pseudo-NMIs are enabled.

However, those helpers are called in between a pair of `local_daif_save()`
and `local_daif_restore()`, which already configure the PMR as expected.
Effectively, `arm_cpuidle_save_irq_context()` is a no-op here,
even when using pseudo-NMIs, and `arm_cpuidle_restore_irq_context()`
would not restore proper interrupt masking configuration early enough
if there were unexpected changes during suspend or resume.
(This can be observed with Trusted Firmware A (TF-A) at EL3 handling
suspend through PSCI. Even though it should not be the case, TF-A can
reset `ICC_PMR_EL1` during CPU_SUSPEND, thus resuming the kernel
with an inconsistent priority mask value on hardware implementing
more than the minimum number of priority levels, such as Morello.)

Thus : remove the cpuidle context helpers as they do not do anything,
but keep the comment mentioning the need for interrupts to reach the CPU
if we are using pseudo-NMIs.

Signed-off-by: Ada Couprie Diaz <ada.coupriediaz at arm.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin at arm.com>
---
 arch/arm64/kernel/suspend.c | 12 +++---------
 1 file changed, 3 insertions(+), 9 deletions(-)

diff --git a/arch/arm64/kernel/suspend.c b/arch/arm64/kernel/suspend.c
index eaaff94329cd..c41724a40b75 100644
--- a/arch/arm64/kernel/suspend.c
+++ b/arch/arm64/kernel/suspend.c
@@ -99,7 +99,6 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	int ret = 0;
 	unsigned long flags;
 	struct sleep_stack_data state;
-	struct arm_cpuidle_irq_context context;
 
 	/*
 	 * Some portions of CPU state (e.g. PSTATE.{PAN,DIT}) are initialized
@@ -121,6 +120,9 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	 * Strictly speaking the trace_hardirqs_off() here is superfluous,
 	 * hardirqs should be firmly off by now. This really ought to use
 	 * something like raw_local_daif_save().
+	 *
+	 * This also unmasks interrupts in PMR in order to reliably
+	 * resume if we're using pseudo-NMIs.
 	 */
 	flags = local_daif_save();
 
@@ -131,12 +133,6 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 	 */
 	pause_graph_tracing();
 
-	/*
-	 * Switch to using DAIF.IF instead of PMR in order to reliably
-	 * resume if we're using pseudo-NMIs.
-	 */
-	arm_cpuidle_save_irq_context(&context);
-
 	ct_cpuidle_enter();
 
 	if (__cpu_suspend_enter(&state)) {
@@ -159,8 +155,6 @@ int cpu_suspend(unsigned long arg, int (*fn)(unsigned long))
 		__cpu_suspend_exit();
 	}
 
-	arm_cpuidle_restore_irq_context(&context);
-
 	unpause_graph_tracing();
 
 	/*
-- 
2.34.1