arm64: irqchip/gic-v3: Select priorities at boot time

The distributor and PMR/RPR can present different views of the interrupt
priority space dependent upon the values of GICD_CTLR.DS and
SCR_EL3.FIQ. Currently we treat the distributor's view of the priority
space as canonical, and when the two differ we change the way we handle
values in the PMR/RPR, using the `gic_nonsecure_priorities` static key
to decide what to do.

This approach works, but it's sub-optimal. When using pseudo-NMI we
manipulate the distributor rarely, and we manipulate the PMR/RPR
registers very frequently in code spread out throughout the kernel (e.g.
local_irq_{save,restore}()). It would be nicer if we could use fixed
values for the PMR/RPR, and dynamically choose the values programmed
into the distributor.

This patch changes the GICv3 driver and arm64 code accordingly. PMR
values are chosen at compile time, and the GICv3 driver determines the
appropriate values to program into the distributor at boot time. This
removes the need for the `gic_nonsecure_priorities` static key and
results in smaller and better generated code for saving/restoring the
irqflags.

Before this patch, local_irq_disable() compiles to:

| 0000000000000000 <outlined_local_irq_disable>:
|    0:   d503201f        nop
|    4:   d50343df        msr     daifset, #0x3
|    8:   d65f03c0        ret
|    c:   d503201f        nop
|   10:   d2800c00        mov     x0, #0x60                       // #96
|   14:   d5184600        msr     icc_pmr_el1, x0
|   18:   d65f03c0        ret
|   1c:   d2801400        mov     x0, #0xa0                       // #160
|   20:   17fffffd        b       14 <outlined_local_irq_disable+0x14>

After this patch, local_irq_disable() compiles to:

| 0000000000000000 <outlined_local_irq_disable>:
|    0:   d503201f        nop
|    4:   d50343df        msr     daifset, #0x3
|    8:   d65f03c0        ret
|    c:   d2801800        mov     x0, #0xc0                       // #192
|   10:   d5184600        msr     icc_pmr_el1, x0
|   14:   d65f03c0        ret

... with 3 fewer instructions per call.

For defconfig + CONFIG_PSEUDO_NMI=y, this results in a minor saving of
~4K of text, and will make it easier to make further improvements to the
way we manipulate irqflags and DAIF bits.

Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Cc: Alexandru Elisei <alexandru.elisei@arm.com>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>
Reviewed-by: Marc Zyngier <maz@kernel.org>
Tested-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20240617111841.2529370-6-mark.rutland@arm.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 6 insertions, 29 deletions

diff --git a/arch/arm64/include/asm/ptrace.h b/arch/arm64/include/asm/ptrace.h
index 47ec58031f11..0abe975d68a8 100644
--- a/arch/arm64/include/asm/ptrace.h
+++ b/arch/arm64/include/asm/ptrace.h
@@ -21,35 +21,12 @@
 #define INIT_PSTATE_EL2 \
 	(PSR_D_BIT | PSR_A_BIT | PSR_I_BIT | PSR_F_BIT | PSR_MODE_EL2h)
 
-/*
- * 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.
- *
- * Some code sections either automatically switch back to PSR.I or explicitly
- * require to not use priority masking. If bit GIC_PRIO_PSR_I_SET is included
- * in 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			0xe0
-#define __GIC_PRIO_IRQOFF		(GIC_PRIO_IRQON & ~0x80)
-#define __GIC_PRIO_IRQOFF_NS		0xa0
-#define GIC_PRIO_PSR_I_SET		(1 << 4)
-
-#define GIC_PRIO_IRQOFF							\
-	({								\
-		extern struct static_key_false gic_nonsecure_priorities;\
-		u8 __prio = __GIC_PRIO_IRQOFF;				\
-									\
-		if (static_branch_unlikely(&gic_nonsecure_priorities))	\
-			__prio = __GIC_PRIO_IRQOFF_NS;			\
-									\
-		__prio;							\
-	})
+#include <linux/irqchip/arm-gic-v3-prio.h>
+
+#define GIC_PRIO_IRQON		GICV3_PRIO_UNMASKED
+#define GIC_PRIO_IRQOFF		GICV3_PRIO_IRQ
+
+#define GIC_PRIO_PSR_I_SET	GICV3_PRIO_PSR_I_SET
 
 /* Additional SPSR bits not exposed in the UABI */
 #define PSR_MODE_THREAD_BIT	(1 << 0)