KVM: arm64: Introduce __pkvm_vcpu_{load,put}()

Rather than look-up the hyp vCPU on every run hypercall at EL2,
introduce a per-CPU 'loaded_hyp_vcpu' tracking variable which is updated
by a pair of load/put hypercalls called directly from
kvm_arch_vcpu_{load,put}() when pKVM is enabled.

Tested-by: Fuad Tabba <tabba@google.com>
Reviewed-by: Fuad Tabba <tabba@google.com>
Signed-off-by: Quentin Perret <qperret@google.com>
Link: https://lore.kernel.org/r/20241218194059.3670226-10-qperret@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: Marc Zyngier

arch/arm64/include/asm/kvm_asm.h

@@ -79,6 +79,8 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_init_vm,
 	__KVM_HOST_SMCCC_FUNC___pkvm_init_vcpu,
 	__KVM_HOST_SMCCC_FUNC___pkvm_teardown_vm,
+	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_load,
+	__KVM_HOST_SMCCC_FUNC___pkvm_vcpu_put,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]

arch/arm64/kvm/arm.c

@@ -619,12 +619,26 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)
 
 	kvm_arch_vcpu_load_debug_state_flags(vcpu);
 
+	if (is_protected_kvm_enabled()) {
+		kvm_call_hyp_nvhe(__pkvm_vcpu_load,
+				  vcpu->kvm->arch.pkvm.handle,
+				  vcpu->vcpu_idx, vcpu->arch.hcr_el2);
+		kvm_call_hyp(__vgic_v3_restore_vmcr_aprs,
+			     &vcpu->arch.vgic_cpu.vgic_v3);
+	}
+
 	if (!cpumask_test_cpu(cpu, vcpu->kvm->arch.supported_cpus))
 		vcpu_set_on_unsupported_cpu(vcpu);
 }
 
 void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
 {
+	if (is_protected_kvm_enabled()) {
+		kvm_call_hyp(__vgic_v3_save_vmcr_aprs,
+			     &vcpu->arch.vgic_cpu.vgic_v3);
+		kvm_call_hyp_nvhe(__pkvm_vcpu_put);
+	}
+
 	kvm_arch_vcpu_put_debug_state_flags(vcpu);
 	kvm_arch_vcpu_put_fp(vcpu);
 	if (has_vhe())

arch/arm64/kvm/hyp/include/nvhe/pkvm.h

@@ -20,6 +20,12 @@ struct pkvm_hyp_vcpu {
 
 	/* Backpointer to the host's (untrusted) vCPU instance. */
 	struct kvm_vcpu *host_vcpu;
+
+	/*
+	 * If this hyp vCPU is loaded, then this is a backpointer to the
+	 * per-cpu pointer tracking us. Otherwise, NULL if not loaded.
+	 */
+	struct pkvm_hyp_vcpu **loaded_hyp_vcpu;
 };
 
 /*
@@ -69,6 +75,7 @@ int __pkvm_teardown_vm(pkvm_handle_t handle);
 struct pkvm_hyp_vcpu *pkvm_load_hyp_vcpu(pkvm_handle_t handle,
 					 unsigned int vcpu_idx);
 void pkvm_put_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu);
+struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void);
 
 struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle);
 void put_pkvm_hyp_vm(struct pkvm_hyp_vm *hyp_vm);

arch/arm64/kvm/hyp/nvhe/hyp-main.c

@@ -141,16 +141,46 @@ static void sync_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 		host_cpu_if->vgic_lr[i] = hyp_cpu_if->vgic_lr[i];
 }
 
+static void handle___pkvm_vcpu_load(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(pkvm_handle_t, handle, host_ctxt, 1);
+	DECLARE_REG(unsigned int, vcpu_idx, host_ctxt, 2);
+	DECLARE_REG(u64, hcr_el2, host_ctxt, 3);
+	struct pkvm_hyp_vcpu *hyp_vcpu;
+
+	if (!is_protected_kvm_enabled())
+		return;
+
+	hyp_vcpu = pkvm_load_hyp_vcpu(handle, vcpu_idx);
+	if (!hyp_vcpu)
+		return;
+
+	if (pkvm_hyp_vcpu_is_protected(hyp_vcpu)) {
+		/* Propagate WFx trapping flags */
+		hyp_vcpu->vcpu.arch.hcr_el2 &= ~(HCR_TWE | HCR_TWI);
+		hyp_vcpu->vcpu.arch.hcr_el2 |= hcr_el2 & (HCR_TWE | HCR_TWI);
+	}
+}
+
+static void handle___pkvm_vcpu_put(struct kvm_cpu_context *host_ctxt)
+{
+	struct pkvm_hyp_vcpu *hyp_vcpu;
+
+	if (!is_protected_kvm_enabled())
+		return;
+
+	hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
+	if (hyp_vcpu)
+		pkvm_put_hyp_vcpu(hyp_vcpu);
+}
+
 static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(struct kvm_vcpu *, host_vcpu, host_ctxt, 1);
 	int ret;
 
-	host_vcpu = kern_hyp_va(host_vcpu);
-
 	if (unlikely(is_protected_kvm_enabled())) {
-		struct pkvm_hyp_vcpu *hyp_vcpu;
-		struct kvm *host_kvm;
+		struct pkvm_hyp_vcpu *hyp_vcpu = pkvm_get_loaded_hyp_vcpu();
 
 		/*
 		 * KVM (and pKVM) doesn't support SME guests for now, and
@@ -163,9 +193,6 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
 			goto out;
 		}
 
-		host_kvm = kern_hyp_va(host_vcpu->kvm);
-		hyp_vcpu = pkvm_load_hyp_vcpu(host_kvm->arch.pkvm.handle,
-					      host_vcpu->vcpu_idx);
 		if (!hyp_vcpu) {
 			ret = -EINVAL;
 			goto out;
@@ -176,12 +203,10 @@ static void handle___kvm_vcpu_run(struct kvm_cpu_context *host_ctxt)
 		ret = __kvm_vcpu_run(&hyp_vcpu->vcpu);
 
 		sync_hyp_vcpu(hyp_vcpu);
-		pkvm_put_hyp_vcpu(hyp_vcpu);
 	} else {
 		/* The host is fully trusted, run its vCPU directly. */
-		ret = __kvm_vcpu_run(host_vcpu);
+		ret = __kvm_vcpu_run(kern_hyp_va(host_vcpu));
 	}
-
 out:
 	cpu_reg(host_ctxt, 1) =  ret;
 }
@@ -409,6 +434,8 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_init_vm),
 	HANDLE_FUNC(__pkvm_init_vcpu),
 	HANDLE_FUNC(__pkvm_teardown_vm),
+	HANDLE_FUNC(__pkvm_vcpu_load),
+	HANDLE_FUNC(__pkvm_vcpu_put),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)

arch/arm64/kvm/hyp/nvhe/pkvm.c

@@ -23,6 +23,12 @@ unsigned int kvm_arm_vmid_bits;
 
 unsigned int kvm_host_sve_max_vl;
 
+/*
+ * The currently loaded hyp vCPU for each physical CPU. Used only when
+ * protected KVM is enabled, but for both protected and non-protected VMs.
+ */
+static DEFINE_PER_CPU(struct pkvm_hyp_vcpu *, loaded_hyp_vcpu);
+
 /*
  * Set trap register values based on features in ID_AA64PFR0.
  */
@@ -306,15 +312,30 @@ struct pkvm_hyp_vcpu *pkvm_load_hyp_vcpu(pkvm_handle_t handle,
 	struct pkvm_hyp_vcpu *hyp_vcpu = NULL;
 	struct pkvm_hyp_vm *hyp_vm;
 
+	/* Cannot load a new vcpu without putting the old one first. */
+	if (__this_cpu_read(loaded_hyp_vcpu))
+		return NULL;
+
 	hyp_spin_lock(&vm_table_lock);
 	hyp_vm = get_vm_by_handle(handle);
 	if (!hyp_vm || hyp_vm->nr_vcpus <= vcpu_idx)
 		goto unlock;
 
 	hyp_vcpu = hyp_vm->vcpus[vcpu_idx];
+
+	/* Ensure vcpu isn't loaded on more than one cpu simultaneously. */
+	if (unlikely(hyp_vcpu->loaded_hyp_vcpu)) {
+		hyp_vcpu = NULL;
+		goto unlock;
+	}
+
+	hyp_vcpu->loaded_hyp_vcpu = this_cpu_ptr(&loaded_hyp_vcpu);
 	hyp_page_ref_inc(hyp_virt_to_page(hyp_vm));
 unlock:
 	hyp_spin_unlock(&vm_table_lock);
+
+	if (hyp_vcpu)
+		__this_cpu_write(loaded_hyp_vcpu, hyp_vcpu);
 	return hyp_vcpu;
 }
 
@@ -323,10 +344,18 @@ void pkvm_put_hyp_vcpu(struct pkvm_hyp_vcpu *hyp_vcpu)
 	struct pkvm_hyp_vm *hyp_vm = pkvm_hyp_vcpu_to_hyp_vm(hyp_vcpu);
 
 	hyp_spin_lock(&vm_table_lock);
+	hyp_vcpu->loaded_hyp_vcpu = NULL;
+	__this_cpu_write(loaded_hyp_vcpu, NULL);
 	hyp_page_ref_dec(hyp_virt_to_page(hyp_vm));
 	hyp_spin_unlock(&vm_table_lock);
 }
 
+struct pkvm_hyp_vcpu *pkvm_get_loaded_hyp_vcpu(void)
+{
+	return __this_cpu_read(loaded_hyp_vcpu);
+
+}
+
 struct pkvm_hyp_vm *get_pkvm_hyp_vm(pkvm_handle_t handle)
 {
 	struct pkvm_hyp_vm *hyp_vm;

arch/arm64/kvm/vgic/vgic-v3.c

@@ -734,7 +734,8 @@ void vgic_v3_load(struct kvm_vcpu *vcpu)
 {
 	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
 
-	kvm_call_hyp(__vgic_v3_restore_vmcr_aprs, cpu_if);
+	if (likely(!is_protected_kvm_enabled()))
+		kvm_call_hyp(__vgic_v3_restore_vmcr_aprs, cpu_if);
 
 	if (has_vhe())
 		__vgic_v3_activate_traps(cpu_if);
@@ -746,7 +747,8 @@ void vgic_v3_put(struct kvm_vcpu *vcpu)
 {
 	struct vgic_v3_cpu_if *cpu_if = &vcpu->arch.vgic_cpu.vgic_v3;
 
-	kvm_call_hyp(__vgic_v3_save_vmcr_aprs, cpu_if);
+	if (likely(!is_protected_kvm_enabled()))
+		kvm_call_hyp(__vgic_v3_save_vmcr_aprs, cpu_if);
 	WARN_ON(vgic_v4_put(vcpu));
 
 	if (has_vhe())