[PATCH v1 07/11] KVM: s390: Move all code into kvm_arch_prepare_memory_region()

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

Move all code from kvm_arch_commit_memory_region() into
kvm_arch_prepare_memory_region(). This allows the function to fail
gracefully if needed. The previous behaviour was to print a warning and
continue execution with page tables incosistent with the memslots.

The new kvm_s390_mmu_cache_extended_topup() function is used to
guarantee that the necessary DAT table updates can be performed
successfully.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
---
 arch/s390/kvm/kvm-s390.c | 124 +++++++++++++++++++--------------------
 1 file changed, 59 insertions(+), 65 deletions(-)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 02c5428ba239..c4196f9af05d 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5766,11 +5766,28 @@ bool kvm_arch_irqchip_in_kernel(struct kvm *kvm)
 }
 
 /* Section: memory related */
+static long cmma_d_count_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
+{
+	union pgste pgste;
+
+	pgste = pgste_get_lock(ptep);
+	if (pgste.cmma_d) {
+		pgste.cmma_d = 0;
+		atomic64_dec(walk->priv);
+	}
+	pgste_set_unlock(ptep, pgste);
+	return 0;
+}
+
 int kvm_arch_prepare_memory_region(struct kvm *kvm,
 				   const struct kvm_memory_slot *old,
 				   struct kvm_memory_slot *new,
 				   enum kvm_mr_change change)
 {
+	const struct dat_walk_ops ops = { .pte_entry = cmma_d_count_pte, };
+	struct kvm_s390_mmu_cache *mc __free(kvm_s390_mmu_cache) = NULL;
+	int rc = 0;
+
 	if (kvm_is_ucontrol(kvm) && new && new->id < KVM_USER_MEM_SLOTS)
 		return -EINVAL;
 
@@ -5785,6 +5802,10 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 		 * and munmap() stuff in this slot after doing this call at any
 		 * time.
 		 */
+		if (change != KVM_MR_MOVE && change != KVM_MR_CREATE) {
+			WARN(1, "Unknown KVM MR CHANGE: %d\n", change);
+			return -EINVAL;
+		}
 		if (new->userspace_addr & ~PAGE_MASK)
 			return -EINVAL;
 		if ((new->base_gfn + new->npages) * PAGE_SIZE > kvm->arch.mem_limit)
@@ -5793,57 +5814,27 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 			return -EINVAL;
 	}
 
-	if (!kvm->arch.migration_mode)
-		return 0;
-
-	/*
-	 * Turn off migration mode when:
-	 * - userspace creates a new memslot with dirty logging off,
-	 * - userspace modifies an existing memslot (MOVE or FLAGS_ONLY) and
-	 *   dirty logging is turned off.
-	 * Migration mode expects dirty page logging being enabled to store
-	 * its dirty bitmap.
-	 */
-	if (change != KVM_MR_DELETE &&
-	    !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
-		WARN(kvm_s390_vm_stop_migration(kvm),
-		     "Failed to stop migration mode");
-
-	return 0;
-}
-
-static long cmma_d_count_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
-{
-	union pgste pgste;
-
-	pgste = pgste_get_lock(ptep);
-	if (pgste.cmma_d) {
-		pgste.cmma_d = 0;
-		atomic64_dec(walk->priv);
+	if (kvm->arch.migration_mode) {
+		/*
+		 * Turn off migration mode when:
+		 * - userspace creates a new memslot with dirty logging off,
+		 * - userspace modifies an existing memslot (MOVE or FLAGS_ONLY)
+		 *   and dirty logging is turned off.
+		 * Migration mode expects dirty page logging being enabled to
+		 * store its dirty bitmap.
+		 */
+		if (change != KVM_MR_DELETE &&
+		    !(new->flags & KVM_MEM_LOG_DIRTY_PAGES))
+			WARN(kvm_s390_vm_stop_migration(kvm),
+			     "Failed to stop migration mode");
 	}
-	pgste_set_unlock(ptep, pgste);
-	return 0;
-}
-
-void kvm_arch_commit_memory_region(struct kvm *kvm,
-				struct kvm_memory_slot *old,
-				const struct kvm_memory_slot *new,
-				enum kvm_mr_change change)
-{
-	const struct dat_walk_ops ops = { .pte_entry = cmma_d_count_pte, };
-	struct kvm_s390_mmu_cache *mc __free(kvm_s390_mmu_cache) = NULL;
-	int rc = 0;
-
-	guard(mutex)(&kvm->slots_arch_lock);
 
 	if (change == KVM_MR_FLAGS_ONLY)
-		return;
+		return 0;
 
 	mc = kvm_s390_new_mmu_cache();
-	if (!mc) {
-		rc = -ENOMEM;
-		goto out;
-	}
+	if (!mc || kvm_s390_mmu_cache_extended_topup(mc))
+		return -ENOMEM;
 
 	scoped_guard(write_lock, &kvm->mmu_lock) {
 		if (kvm->arch.migration_mode && kvm->arch.use_cmma && old) {
@@ -5852,28 +5843,31 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 					    &kvm->arch.cmma_dirty_pages);
 		}
 
-		switch (change) {
-		case KVM_MR_DELETE:
+		if (change == KVM_MR_DELETE || change == KVM_MR_MOVE)
 			rc = dat_delete_slot(mc, kvm->arch.gmap->asce, old->base_gfn, old->npages);
-			break;
-		case KVM_MR_MOVE:
-			rc = dat_delete_slot(mc, kvm->arch.gmap->asce, old->base_gfn, old->npages);
-			if (rc)
-				break;
-			fallthrough;
-		case KVM_MR_CREATE:
+		if (!rc && (change == KVM_MR_MOVE || change == KVM_MR_CREATE))
 			rc = dat_create_slot(mc, kvm->arch.gmap->asce, new->base_gfn, new->npages);
-			break;
-		case KVM_MR_FLAGS_ONLY:
-			break;
-		default:
-			WARN(1, "Unknown KVM MR CHANGE: %d\n", change);
-		}
 	}
-out:
-	if (rc)
-		pr_warn("failed to commit memory region\n");
-	return;
+
+	/*
+	 * dat_{create,delete}_slot() can only fail in two cases:
+	 * - Internal consistency error in the gmap DAT tables
+	 * - Out of memory while allocating DAT tables
+	 * The first case should not be possible in general, and is a symptom of
+	 * a serious KVM bug; the second should also be impossible because the
+	 * mmu cache has been filled to the brim, and has more than enough
+	 * capacity to handle the worst cases. Hence it is safe to put this
+	 * KVM_BUG_ON() here, as it should not be triggerable unless some
+	 * serious bug has occurred somewhere else.
+	 */
+	return KVM_BUG_ON(rc, kvm);
+}
+
+void kvm_arch_commit_memory_region(struct kvm *kvm,
+				   struct kvm_memory_slot *old,
+				   const struct kvm_memory_slot *new,
+				   enum kvm_mr_change change)
+{
 }
 
 /**
-- 
2.55.0