KVM: arm64: Add accessor for per-CPU state

In order to facilitate the introduction of new per-CPU state,
add a new host_data_ptr() helped that hides some of the per-CPU
verbosity, and make it easier to move that state around in the
future.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>

1 files changed, 37 insertions, 0 deletions

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 9e8a496fb284..f41db42529df 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -530,6 +530,17 @@ struct kvm_cpu_context {
 	u64 *vncr_array;
 };
 
+/*
+ * This structure is instantiated on a per-CPU basis, and contains
+ * data that is:
+ *
+ * - tied to a single physical CPU, and
+ * - either have a lifetime that does not extend past vcpu_put()
+ * - or is an invariant for the lifetime of the system
+ *
+ * Use host_data_ptr(field) as a way to access a pointer to such a
+ * field.
+ */
 struct kvm_host_data {
 	struct kvm_cpu_context host_ctxt;
 };
@@ -1168,6 +1179,32 @@ struct kvm_vcpu *kvm_mpidr_to_vcpu(struct kvm *kvm, unsigned long mpidr);
 
 DECLARE_KVM_HYP_PER_CPU(struct kvm_host_data, kvm_host_data);
 
+/*
+ * How we access per-CPU host data depends on the where we access it from,
+ * and the mode we're in:
+ *
+ * - VHE and nVHE hypervisor bits use their locally defined instance
+ *
+ * - the rest of the kernel use either the VHE or nVHE one, depending on
+ *   the mode we're running in.
+ *
+ *   Unless we're in protected mode, fully deprivileged, and the nVHE
+ *   per-CPU stuff is exclusively accessible to the protected EL2 code.
+ *   In this case, the EL1 code uses the *VHE* data as its private state
+ *   (which makes sense in a way as there shouldn't be any shared state
+ *   between the host and the hypervisor).
+ *
+ * Yes, this is all totally trivial. Shoot me now.
+ */
+#if defined(__KVM_NVHE_HYPERVISOR__) || defined(__KVM_VHE_HYPERVISOR__)
+#define host_data_ptr(f)	(&this_cpu_ptr(&kvm_host_data)->f)
+#else
+#define host_data_ptr(f)						\
+	(static_branch_unlikely(&kvm_protected_mode_initialized) ?	\
+	 &this_cpu_ptr(&kvm_host_data)->f :				\
+	 &this_cpu_ptr_hyp_sym(kvm_host_data)->f)
+#endif
+
 static inline void kvm_init_host_cpu_context(struct kvm_cpu_context *cpu_ctxt)
 {
 	/* The host's MPIDR is immutable, so let's set it up at boot time */