arm64: ptrace: Provide definitions for PMR values

Introduce fixed values for PMR that are going to be used to mask and
unmask interrupts by priority.

The current priority given to GIC interrupts is 0xa0, so clearing PMR's
most significant bit is enough to mask interrupts.
Signed-off-by: Julien Thierry <julien.thierry@arm.com>
Suggested-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/include/asm/ptrace.h

@@ -25,6 +25,18 @@
 #define CurrentEL_EL1		(1 << 2)
 #define CurrentEL_EL2		(2 << 2)
 
+/*
+ * PMR values used to mask/unmask interrupts.
+ *
+ * GIC priority masking works as follows: if an IRQ's priority is a higher value
+ * than the value held in PMR, that IRQ is masked. Lowering the value of PMR
+ * means masking more IRQs (or at least that the same IRQs remain masked).
+ *
+ * To mask interrupts, we clear the most significant bit of PMR.
+ */
+#define GIC_PRIO_IRQON		0xf0
+#define GIC_PRIO_IRQOFF		(GIC_PRIO_IRQON & ~0x80)
+
 /* Additional SPSR bits not exposed in the UABI */
 #define PSR_IL_BIT		(1 << 20)