Merge branch kvm-arm64/smccc-filter-cleanups into kvmarm/next

* kvm-arm64/smccc-filter-cleanups:
  : Cleanup the management of KVM's SMCCC maple tree
  :
  : Avoid the cost of maintaining the SMCCC filter maple tree if userspace
  : hasn't writen a rule to the filter. While at it, rip out the now
  : unnecessary VM flag to indicate whether or not the SMCCC filter was
  : configured.
  KVM: arm64: Use mtree_empty() to determine if SMCCC filter configured
  KVM: arm64: Only insert reserved ranges when SMCCC filter is used
  KVM: arm64: Add a predicate for testing if SMCCC filter is configured

Signed-off-by: Oliver Upton <oliver.upton@linux.dev>

2 files changed, 23 insertions, 15 deletions

diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index c3a17888f183..6d3f301af72a 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -239,10 +239,8 @@ struct kvm_arch {
 #define KVM_ARCH_FLAG_VM_COUNTER_OFFSET			5
 	/* Timer PPIs made immutable */
 #define KVM_ARCH_FLAG_TIMER_PPIS_IMMUTABLE		6
-	/* SMCCC filter initialized for the VM */
-#define KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED		7
 	/* Initial ID reg values loaded */
-#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		8
+#define KVM_ARCH_FLAG_ID_REGS_INITIALIZED		7
 	unsigned long flags;
 
 	/* VM-wide vCPU feature set */
diff --git a/arch/arm64/kvm/hypercalls.c b/arch/arm64/kvm/hypercalls.c
index 1b79219c590c..5763d979d8ca 100644
--- a/arch/arm64/kvm/hypercalls.c
+++ b/arch/arm64/kvm/hypercalls.c
@@ -133,12 +133,10 @@ static bool kvm_smccc_test_fw_bmap(struct kvm_vcpu *vcpu, u32 func_id)
 						   ARM_SMCCC_SMC_64,		\
 						   0, ARM_SMCCC_FUNC_MASK)
 
-static void init_smccc_filter(struct kvm *kvm)
+static int kvm_smccc_filter_insert_reserved(struct kvm *kvm)
 {
 	int r;
 
-	mt_init(&kvm->arch.smccc_filter);
-
 	/*
 	 * Prevent userspace from handling any SMCCC calls in the architecture
 	 * range, avoiding the risk of misrepresenting Spectre mitigation status
@@ -148,14 +146,25 @@ static void init_smccc_filter(struct kvm *kvm)
 			       SMC32_ARCH_RANGE_BEGIN, SMC32_ARCH_RANGE_END,
 			       xa_mk_value(KVM_SMCCC_FILTER_HANDLE),
 			       GFP_KERNEL_ACCOUNT);
-	WARN_ON_ONCE(r);
+	if (r)
+		goto out_destroy;
 
 	r = mtree_insert_range(&kvm->arch.smccc_filter,
 			       SMC64_ARCH_RANGE_BEGIN, SMC64_ARCH_RANGE_END,
 			       xa_mk_value(KVM_SMCCC_FILTER_HANDLE),
 			       GFP_KERNEL_ACCOUNT);
-	WARN_ON_ONCE(r);
+	if (r)
+		goto out_destroy;
 
+	return 0;
+out_destroy:
+	mtree_destroy(&kvm->arch.smccc_filter);
+	return r;
+}
+
+static bool kvm_smccc_filter_configured(struct kvm *kvm)
+{
+	return !mtree_empty(&kvm->arch.smccc_filter);
 }
 
 static int kvm_smccc_set_filter(struct kvm *kvm, struct kvm_smccc_filter __user *uaddr)
@@ -184,13 +193,14 @@ static int kvm_smccc_set_filter(struct kvm *kvm, struct kvm_smccc_filter __user
 		goto out_unlock;
 	}
 
+	if (!kvm_smccc_filter_configured(kvm)) {
+		r = kvm_smccc_filter_insert_reserved(kvm);
+		if (WARN_ON_ONCE(r))
+			goto out_unlock;
+	}
+
 	r = mtree_insert_range(&kvm->arch.smccc_filter, start, end,
 			       xa_mk_value(filter.action), GFP_KERNEL_ACCOUNT);
-	if (r)
-		goto out_unlock;
-
-	set_bit(KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags);
-
 out_unlock:
 	mutex_unlock(&kvm->arch.config_lock);
 	return r;
@@ -201,7 +211,7 @@ static u8 kvm_smccc_filter_get_action(struct kvm *kvm, u32 func_id)
 	unsigned long idx = func_id;
 	void *val;
 
-	if (!test_bit(KVM_ARCH_FLAG_SMCCC_FILTER_CONFIGURED, &kvm->arch.flags))
+	if (!kvm_smccc_filter_configured(kvm))
 		return KVM_SMCCC_FILTER_HANDLE;
 
 	/*
@@ -387,7 +397,7 @@ void kvm_arm_init_hypercalls(struct kvm *kvm)
 	smccc_feat->std_hyp_bmap = KVM_ARM_SMCCC_STD_HYP_FEATURES;
 	smccc_feat->vendor_hyp_bmap = KVM_ARM_SMCCC_VENDOR_HYP_FEATURES;
 
-	init_smccc_filter(kvm);
+	mt_init(&kvm->arch.smccc_filter);
 }
 
 void kvm_arm_teardown_hypercalls(struct kvm *kvm)