arm64: Lower priority mask for GIC_PRIO_IRQON

On a system with two security states, if SCR_EL3.FIQ is cleared,
non-secure IRQ priorities get shifted to fit the secure view but
priority masks aren't.

On such system, it turns out that GIC_PRIO_IRQON masks the priority of
normal interrupts, which obviously ends up in a hang.

Increase GIC_PRIO_IRQON value (i.e. lower priority) to make sure
interrupts are not blocked by it.

Cc: Oleg Nesterov <oleg@redhat.com>
Fixes: bd82d4bd ("arm64: Fix incorrect irqflag restore for priority masking")
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Julien Thierry <julien.thierry.kdev@gmail.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
[will: fixed Fixes: tag]
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/arch_gicv3.h

@@ -155,6 +155,12 @@ static inline void gic_pmr_mask_irqs(void)
 	BUILD_BUG_ON(GICD_INT_DEF_PRI < (GIC_PRIO_IRQOFF |
 					 GIC_PRIO_PSR_I_SET));
 	BUILD_BUG_ON(GICD_INT_DEF_PRI >= GIC_PRIO_IRQON);
+	/*
+	 * Need to make sure IRQON allows IRQs when SCR_EL3.FIQ is cleared
+	 * and non-secure PMR accesses are not subject to the shifts that
+	 * are applied to IRQ priorities
+	 */
+	BUILD_BUG_ON((0x80 | (GICD_INT_DEF_PRI >> 1)) >= GIC_PRIO_IRQON);
 	gic_write_pmr(GIC_PRIO_IRQOFF);
 }
 

arch/arm64/include/asm/ptrace.h

@@ -30,7 +30,7 @@
  * in the  the priority mask, it indicates that PSR.I should be set and
  * interrupt disabling temporarily does not rely on IRQ priorities.
  */
-#define GIC_PRIO_IRQON			0xc0
+#define GIC_PRIO_IRQON			0xe0
 #define GIC_PRIO_IRQOFF			(GIC_PRIO_IRQON & ~0x80)
 #define GIC_PRIO_PSR_I_SET		(1 << 4)