[PATCH v3 4/5] KVM: s390: vsie: Add missing radix_tree_preload() in _gaccess_shadow_fault()

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

Add missing radix_tree_preload() in _gaccess_shadow_fault() to
guarantee forward progress. The core of _gaccess_shadow_fault() has
been split into ___gaccess_shadow_fault() in order to simplify locking.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
CC: stable@vger.kernel.org # 7.1
---
 arch/s390/kvm/gaccess.c | 57 +++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 22 deletions(-)

diff --git a/arch/s390/kvm/gaccess.c b/arch/s390/kvm/gaccess.c
index 20e28b183c1a..0584fc91606f 100644
--- a/arch/s390/kvm/gaccess.c
+++ b/arch/s390/kvm/gaccess.c
@@ -1582,35 +1582,48 @@ static int _gaccess_do_shadow(struct kvm_s390_mmu_cache *mc, struct gmap *sg,
 	return _do_shadow_crste(sg, saddr, host, table, entries + LEVEL_MEM, w->p);
 }
 
-static inline int _gaccess_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg, gpa_t saddr,
-					unsigned long seq, struct pgtwalk *walk)
+static inline int ___gaccess_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg, gpa_t saddr,
+					  unsigned long seq, struct pgtwalk *walk)
 {
 	struct gmap *parent;
 	int rc;
 
-	if (kvm_s390_array_needs_retry_unsafe(vcpu->kvm, seq, walk->raw_entries))
+	if (kvm_s390_array_needs_retry_safe(vcpu->kvm, seq, walk->raw_entries))
 		return -EAGAIN;
-again:
-	rc = kvm_s390_mmu_cache_topup(vcpu->arch.mc);
-	if (rc)
-		return rc;
-	scoped_guard(read_lock, &vcpu->kvm->mmu_lock) {
-		if (kvm_s390_array_needs_retry_safe(vcpu->kvm, seq, walk->raw_entries))
-			return -EAGAIN;
-		parent = READ_ONCE(sg->parent);
-		if (!parent)
+	parent = READ_ONCE(sg->parent);
+	if (!parent)
+		return -EAGAIN;
+	scoped_guard(spinlock, &parent->children_lock) {
+		if (READ_ONCE(sg->parent) != parent)
 			return -EAGAIN;
-		scoped_guard(spinlock, &parent->children_lock) {
-			if (READ_ONCE(sg->parent) != parent)
-				return -EAGAIN;
-			sg->invalidated = false;
-			rc = _gaccess_do_shadow(vcpu->arch.mc, sg, saddr, walk);
-		}
-		if (rc == -ENOMEM)
-			goto again;
-		if (!rc)
-			kvm_s390_release_faultin_array(vcpu->kvm, walk->raw_entries, false);
+		sg->invalidated = false;
+		rc = _gaccess_do_shadow(vcpu->arch.mc, sg, saddr, walk);
 	}
+	if (!rc)
+		kvm_s390_release_faultin_array(vcpu->kvm, walk->raw_entries, false);
+	return rc;
+}
+
+static inline int _gaccess_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg, gpa_t saddr,
+					unsigned long seq, struct pgtwalk *walk)
+{
+	int rc;
+
+	if (kvm_s390_array_needs_retry_unsafe(vcpu->kvm, seq, walk->raw_entries))
+		return -EAGAIN;
+
+	do {
+		rc = kvm_s390_mmu_cache_topup(vcpu->arch.mc);
+		if (rc)
+			return rc;
+		rc = radix_tree_preload(GFP_KERNEL);
+		if (rc)
+			return rc;
+		scoped_guard(read_lock, &vcpu->kvm->mmu_lock)
+			rc = ___gaccess_shadow_fault(vcpu, sg, saddr, seq, walk);
+		radix_tree_preload_end();
+	} while (rc == -ENOMEM);
+
 	return rc;
 }
 
-- 
2.54.0