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, 0 insertions, 5 deletions

diff --git a/arch/arm64/kernel/image-vars.h b/arch/arm64/kernel/image-vars.h
index ba4f8f7d6a91..8f5422ed1b75 100644
--- a/arch/arm64/kernel/image-vars.h
+++ b/arch/arm64/kernel/image-vars.h
@@ -105,11 +105,6 @@ KVM_NVHE_ALIAS(__hyp_stub_vectors);
 KVM_NVHE_ALIAS(vgic_v2_cpuif_trap);
 KVM_NVHE_ALIAS(vgic_v3_cpuif_trap);
 
-#ifdef CONFIG_ARM64_PSEUDO_NMI
-/* Static key checked in GIC_PRIO_IRQOFF. */
-KVM_NVHE_ALIAS(gic_nonsecure_priorities);
-#endif
-
 /* EL2 exception handling */
 KVM_NVHE_ALIAS(__start___kvm_ex_table);
 KVM_NVHE_ALIAS(__stop___kvm_ex_table);