[PATCH v1 6/8] KVM: s390: cmma: Fix dirty tracking when removing memslot

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

When a memslot is removed, all ptes that mapped the slot are cleared or
even deallocated. If this happens while the system is in migration
mode, and if cmma-dirty pages are removed, the cmma-dirty counter will
not reflect reality.

Fix by appropriately decrementing the cmma-dirty counter when removing
a memslot.

Fixes: e38c884df921 ("KVM: s390: Switch to new gmap")
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/kvm-s390.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 512c81eee068..2ac3a9ac4698 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -5792,11 +5792,19 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm,
 	return 0;
 }
 
+static long cmma_d_count_pte(union pte *ptep, gfn_t gfn, gfn_t next, struct dat_walk *walk)
+{
+	if (pgste_of(ptep)->cmma_d)
+		atomic64_dec(walk->priv);
+	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 = NULL;
 	int rc = 0;
 
@@ -5810,6 +5818,12 @@ void kvm_arch_commit_memory_region(struct kvm *kvm,
 	}
 
 	scoped_guard(write_lock, &kvm->mmu_lock) {
+		if (kvm->arch.migration_mode && kvm->arch.use_cmma) {
+			_dat_walk_gfn_range(old->base_gfn, old->base_gfn + old->npages,
+					    kvm->arch.gmap->asce, &ops, DAT_WALK_IGN_HOLES,
+					    &kvm->arch.cmma_dirty_pages);
+		}
+
 		switch (change) {
 		case KVM_MR_DELETE:
 			rc = dat_delete_slot(mc, kvm->arch.gmap->asce, old->base_gfn, old->npages);
-- 
2.55.0