From: David Woodhouse <dwmw@amazon.co.uk>

When kvm_gfn_to_hva_cache_init() is used to cache the address of the
guest pages which KVM needs to access, it uses kvm_memslots(). For
which an RCU read lock is required. Add that around the whole of
the kvm_xen_hvm_set_attr() function.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
---
This should fix the RCU warning reported by the 'kernel test robot'.

Paolo, please let me know if you're prefer to fold this in to the
original patch or whether it's OK as a 17th patch in the series.

I've pushed this on top for now, at
 https://git.infradead.org/users/dwmw2/linux.git/shortlog/refs/heads/xenpv

 arch/x86/kvm/xen.c | 39 ++++++++++++++++++++++++++-------------
 1 file changed, 26 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 4bc9da9fcfb8..3041f774493e 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -219,11 +219,14 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 {
 	struct kvm_vcpu *v;
 	int r = -ENOENT;
+	int idx = srcu_read_lock(&kvm->srcu);
 
 	switch (data->type) {
 	case KVM_XEN_ATTR_TYPE_LONG_MODE:
-		if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode)
-			return -EINVAL;
+		if (!IS_ENABLED(CONFIG_64BIT) && data->u.long_mode) {
+			r = -EINVAL;
+			break;
+		}
 
 		kvm->arch.xen.long_mode = !!data->u.long_mode;
 		r = 0;
@@ -235,8 +238,11 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 
 	case KVM_XEN_ATTR_TYPE_VCPU_INFO:
 		v = kvm_get_vcpu_by_id(kvm, data->u.vcpu_attr.vcpu_id);
-		if (!v)
-			return -EINVAL;
+		if (!v) {
+			r = -EINVAL;
+			break;
+		}
+
 		/* No compat necessary here. */
 		BUILD_BUG_ON(sizeof(struct vcpu_info) !=
 			     sizeof(struct compat_vcpu_info));
@@ -247,7 +253,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 					      data->u.vcpu_attr.gpa,
 					      sizeof(struct vcpu_info));
 		if (r)
-			return r;
+			break;
 
 		v->arch.xen.vcpu_info_set = true;
 		kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
@@ -255,14 +261,16 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 
 	case KVM_XEN_ATTR_TYPE_VCPU_TIME_INFO:
 		v = kvm_get_vcpu_by_id(kvm, data->u.vcpu_attr.vcpu_id);
-		if (!v)
-			return -EINVAL;
+		if (!v) {
+			r = -EINVAL;
+			break;
+		}
 
 		r = kvm_gfn_to_hva_cache_init(kvm, &v->arch.xen.vcpu_time_info_cache,
 					      data->u.vcpu_attr.gpa,
 					      sizeof(struct pvclock_vcpu_time_info));
 		if (r)
-			return r;
+			break;
 
 		v->arch.xen.vcpu_time_info_set = true;
 		kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
@@ -270,14 +278,16 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 
 	case KVM_XEN_ATTR_TYPE_VCPU_RUNSTATE:
 		v = kvm_get_vcpu_by_id(kvm, data->u.vcpu_attr.vcpu_id);
-		if (!v)
-			return -EINVAL;
+		if (!v) {
+			r = -EINVAL;
+			break;
+		}
 
 		r = kvm_gfn_to_hva_cache_init(kvm, &v->arch.xen.runstate_cache,
 					      data->u.vcpu_attr.gpa,
 					      sizeof(struct vcpu_runstate_info));
 		if (r)
-			return r;
+			break;
 
 		v->arch.xen.runstate_set = true;
 		v->arch.xen.current_runstate = RUNSTATE_blocked;
@@ -285,8 +295,10 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		break;
 
 	case KVM_XEN_ATTR_TYPE_UPCALL_VECTOR:
-		if (data->u.vector < 0x10)
-			return -EINVAL;
+		if (data->u.vector < 0x10) {
+			r = -EINVAL;
+			break;
+		}
 
 		kvm->arch.xen.upcall_vector = data->u.vector;
 		r = 0;
@@ -296,6 +308,7 @@ int kvm_xen_hvm_set_attr(struct kvm *kvm, struct kvm_xen_hvm_attr *data)
 		break;
 	}
 
+	srcu_read_unlock(&kvm->srcu, idx);
 	return r;
 }
 
-- 
2.17.1