[PATCH v10 13/25] arm64: daifflags: Include PMR in daifflags restore operations

[Julien Thierry]

The addition of PMR should not bypass the semantics of daifflags.

When DA_F are set, I bit is also set as no interrupts (even of higher
priority) is allowed.

When DA_F are cleared, I bit is cleared and interrupt enabling/disabling
goes through ICC_PMR_EL1.

Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
Reviewed-by: Catalin Marinas <catalin.marinas@xxxxxxx>
Reviewed-by: Marc Zyngier <marc.zyngier@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: James Morse <james.morse@xxxxxxx>
---
 arch/arm64/include/asm/daifflags.h | 50 +++++++++++++++++++++++++++++++++++---
 1 file changed, 46 insertions(+), 4 deletions(-)

diff --git a/arch/arm64/include/asm/daifflags.h b/arch/arm64/include/asm/daifflags.h
index 546bc39..1dd3d7a 100644
--- a/arch/arm64/include/asm/daifflags.h
+++ b/arch/arm64/include/asm/daifflags.h
@@ -18,6 +18,8 @@
 
 #include <linux/irqflags.h>
 
+#include <asm/cpufeature.h>
+
 #define DAIF_PROCCTX		0
 #define DAIF_PROCCTX_NOIRQ	PSR_I_BIT
 
@@ -36,7 +38,13 @@ static inline unsigned long local_daif_save(void)
 {
 	unsigned long flags;
 
-	flags = arch_local_save_flags();
+	flags = read_sysreg(daif);
+
+	if (system_uses_irq_prio_masking()) {
+		/* If IRQs are masked with PMR, reflect it in the flags */
+		if (read_sysreg_s(SYS_ICC_PMR_EL1) <= GIC_PRIO_IRQOFF)
+			flags |= PSR_I_BIT;
+	}
 
 	local_daif_mask();
 
@@ -45,12 +53,46 @@ static inline unsigned long local_daif_save(void)
 
 static inline void local_daif_restore(unsigned long flags)
 {
-	if (!arch_irqs_disabled_flags(flags))
+	bool irq_disabled = flags & PSR_I_BIT;
+
+	if (!irq_disabled) {
 		trace_hardirqs_on();
 
-	arch_local_irq_restore(flags);
+		if (system_uses_irq_prio_masking())
+			arch_local_irq_enable();
+	} else if (!(flags & PSR_A_BIT)) {
+		/*
+		 * If interrupts are disabled but we can take
+		 * asynchronous errors, we can take NMIs
+		 */
+		if (system_uses_irq_prio_masking()) {
+			flags &= ~PSR_I_BIT;
+			/*
+			 * There has been concern that the write to daif
+			 * might be reordered before this write to PMR.
+			 * From the ARM ARM DDI 0487D.a, section D1.7.1
+			 * "Accessing PSTATE fields":
+			 *   Writes to the PSTATE fields have side-effects on
+			 *   various aspects of the PE operation. All of these
+			 *   side-effects are guaranteed:
+			 *     - Not to be visible to earlier instructions in
+			 *       the execution stream.
+			 *     - To be visible to later instructions in the
+			 *       execution stream
+			 *
+			 * Also, writes to PMR are self-synchronizing, so no
+			 * interrupts with a lower priority than PMR is signaled
+			 * to the PE after the write.
+			 *
+			 * So we don't need additional synchronization here.
+			 */
+			arch_local_irq_disable();
+		}
+	}
+
+	write_sysreg(flags, daif);
 
-	if (arch_irqs_disabled_flags(flags))
+	if (irq_disabled)
 		trace_hardirqs_off();
 }
 
-- 
1.9.1