Re: [v3 1/5] KVM: PPC: Book3S HV: Disable page merging in H_SVM_INIT_START

Signed-off-by: Ram Pai <redacted>
---
 arch/powerpc/kvm/book3s_hv_uvmem.c | 96 +++++++++++++++++++++++++++++---------
 1 file changed, 74 insertions(+), 22 deletions(-)

diff --git a/arch/powerpc/kvm/book3s_hv_uvmem.c b/arch/powerpc/kvm/book3s_hv_uvmem.c
index 3d987b1..bfc3841 100644
--- a/arch/powerpc/kvm/book3s_hv_uvmem.c
+++ b/arch/powerpc/kvm/book3s_hv_uvmem.c

@@ -211,6 +211,65 @@ static bool kvmppc_gfn_is_uvmem_pfn(unsigned long gfn, struct kvm *kvm,
 	return false;
 }
 
+static int kvmppc_memslot_page_merge(struct kvm *kvm,
+		struct kvm_memory_slot *memslot, bool merge)
+{
+	unsigned long gfn = memslot->base_gfn;
+	unsigned long end, start = gfn_to_hva(kvm, gfn);
+	int ret = 0;
+	struct vm_area_struct *vma;
+	int merge_flag = (merge) ? MADV_MERGEABLE : MADV_UNMERGEABLE;
+
+	if (kvm_is_error_hva(start))
+		return H_STATE;

+	do {
+		vma = find_vma_intersection(kvm->mm, start, end);
+		if (!vma) {
+			ret = H_STATE;
+			break;
+		}
+		ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
+			  merge_flag, &vma->vm_flags);
+		if (ret) {
+			ret = H_STATE;
+			break;
+		}
+		start = vma->vm_end + 1;
+	} while (end > vma->vm_end);
+
+	up_write(&kvm->mm->mmap_sem);
+	return ret;
+}
+
+static int __kvmppc_page_merge(struct kvm *kvm, bool merge)
+{
+	struct kvm_memslots *slots;
+	struct kvm_memory_slot *memslot;
+	int ret = 0;
+
+	slots = kvm_memslots(kvm);
+	kvm_for_each_memslot(memslot, slots) {
+		ret = kvmppc_memslot_page_merge(kvm, memslot, merge);
+		if (ret)
+			break;
+	}
+	return ret;
+}
+
+static inline int kvmppc_disable_page_merge(struct kvm *kvm)
+{
+	return __kvmppc_page_merge(kvm, false);
+}
+
+static inline int kvmppc_enable_page_merge(struct kvm *kvm)
+{
+	return __kvmppc_page_merge(kvm, true);
+}
+
 unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 {
 	struct kvm_memslots *slots;

@@ -232,11 +291,18 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 		return H_AUTHORITY;
 
 	srcu_idx = srcu_read_lock(&kvm->srcu);
+
+	/* disable page-merging for all memslot */
+	ret = kvmppc_disable_page_merge(kvm);
+	if (ret)
+		goto out;
+
+	/* register the memslot */
 	slots = kvm_memslots(kvm);
 	kvm_for_each_memslot(memslot, slots) {
 		if (kvmppc_uvmem_slot_init(kvm, memslot)) {
 			ret = H_PARAMETER;
-			goto out;
+			break;
 		}
 		ret = uv_register_mem_slot(kvm->arch.lpid,
 					   memslot->base_gfn << PAGE_SHIFT,

@@ -245,9 +311,12 @@ unsigned long kvmppc_h_svm_init_start(struct kvm *kvm)
 		if (ret < 0) {
 			kvmppc_uvmem_slot_free(kvm, memslot);
 			ret = H_PARAMETER;
-			goto out;
+			break;
 		}
 	}
+
+	if (ret)
+		kvmppc_enable_page_merge(kvm);

 out:
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 	return ret;

@@ -384,7 +453,7 @@ static struct page *kvmppc_uvmem_get_page(unsigned long gpa, struct kvm *kvm)
  */
 static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
 		   unsigned long end, unsigned long gpa, struct kvm *kvm,
-		   unsigned long page_shift, bool *downgrade)
+		   unsigned long page_shift)
 {
 	unsigned long src_pfn, dst_pfn = 0;
 	struct migrate_vma mig;

@@ -400,18 +469,6 @@ static int kvmppc_svm_page_in(struct vm_area_struct *vma, unsigned long start,
 	mig.src = &src_pfn;
 	mig.dst = &dst_pfn;
 
-	/*
-	 * We come here with mmap_sem write lock held just for
-	 * ksm_madvise(), otherwise we only need read mmap_sem.
-	 * Hence downgrade to read lock once ksm_madvise() is done.
-	 */
-	ret = ksm_madvise(vma, vma->vm_start, vma->vm_end,
-			  MADV_UNMERGEABLE, &vma->vm_flags);