arm64: KVM: vgic-v2: Add the GICV emulation infrastructure

In order to efficiently perform the GICV access on behalf of the
guest, we need to be able to avoid going back all the way to
the host kernel.

For this, we introduce a new hook in the world switch code,
conveniently placed just after populating the fault info.
At that point, we only have saved/restored the GP registers,
and we can quickly perform all the required checks (data abort,
translation fault, valid faulting syndrome, not an external
abort, not a PTW).

Coming back from the emulation code, we need to skip the emulated
instruction. This involves an additional bit of save/restore in
order to be able to access the guest's PC (and possibly CPSR if
this is a 32bit guest).

At this stage, no emulation code is provided.

Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Reviewed-by: Christoffer Dall <christoffer.dall@linaro.org>
Signed-off-by: Christoffer Dall <christoffer.dall@linaro.org>

include/kvm/arm_vgic.h

@@ -20,6 +20,7 @@
 #include <linux/kvm.h>
 #include <linux/irqreturn.h>
 #include <linux/spinlock.h>
+#include <linux/static_key.h>
 #include <linux/types.h>
 #include <kvm/iodev.h>
 #include <linux/list.h>
@@ -265,6 +266,8 @@ struct vgic_cpu {
 	bool lpis_enabled;
 };
 
+extern struct static_key_false vgic_v2_cpuif_trap;
+
 int kvm_vgic_addr(struct kvm *kvm, unsigned long type, u64 *addr, bool write);
 void kvm_vgic_early_init(struct kvm *kvm);
 int kvm_vgic_create(struct kvm *kvm, u32 type);