[PATCH v1 4/7] KVM: s390: Fix fault-in code

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

Fix the fault-in code so that it does not return success if a
concurrent unmap event invalidated the fault-in process between the
best-effort lockless check and the proper check with lock.

The new behaviour is to retry, like the best-effort lockless check
already did.

This prevents the fault-in handler from returning success without
having actually faulted in the requested page.

Fixes: e907ae530133 ("KVM: s390: Add helper functions for fault handling")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/faultin.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/arch/s390/kvm/faultin.c b/arch/s390/kvm/faultin.c
index ddf0ca71f374..3047dfdc8be4 100644
--- a/arch/s390/kvm/faultin.c
+++ b/arch/s390/kvm/faultin.c
@@ -36,7 +36,7 @@ int kvm_s390_faultin_gfn(struct kvm_vcpu *vcpu, struct kvm *kvm, struct guest_fa
 	struct kvm_s390_mmu_cache *mc = NULL;
 	struct kvm_memory_slot *slot;
 	unsigned long inv_seq;
-	int foll, rc = 0;
+	int foll, rc = -EAGAIN;
 
 	foll = f->write_attempt ? FOLL_WRITE : 0;
 	foll |= f->attempt_pfault ? FOLL_NOWAIT : 0;
@@ -53,7 +53,7 @@ int kvm_s390_faultin_gfn(struct kvm_vcpu *vcpu, struct kvm *kvm, struct guest_fa
 			return 0;
 	}
 
-	while (1) {
+	while (rc == -EAGAIN) {
 		f->valid = false;
 		inv_seq = kvm->mmu_invalidate_seq;
 		/* Pairs with the smp_wmb() in kvm_mmu_invalidate_end(). */
@@ -110,20 +110,19 @@ int kvm_s390_faultin_gfn(struct kvm_vcpu *vcpu, struct kvm *kvm, struct guest_fa
 			if (!mmu_invalidate_retry_gfn(kvm, inv_seq, f->gfn)) {
 				f->valid = true;
 				rc = gmap_link(mc, kvm->arch.gmap, f, slot);
-				kvm_release_faultin_page(kvm, f->page, !!rc, f->write_attempt);
-				f->page = NULL;
 			}
+			kvm_release_faultin_page(kvm, f->page, !!rc, f->write_attempt);
 		}
-		kvm_release_faultin_page(kvm, f->page, true, false);
 
 		if (rc == -ENOMEM) {
 			rc = kvm_s390_mmu_cache_topup(mc);
 			if (rc)
 				return rc;
-		} else if (rc != -EAGAIN) {
-			return rc;
+			rc = -EAGAIN;
 		}
 	}
+
+	return rc;
 }
 
 int kvm_s390_get_guest_page(struct kvm *kvm, struct guest_fault *f, gfn_t gfn, bool w)
-- 
2.54.0