Re: [v4 4/5] KVM: PPC: Book3S HV: retry page migration before erroring-out

I am dropping this patch based on our conversation, where we agreed, we
need to rootcause the migration failure.

On Thu, Jul 23, 2020 at 11:43:44AM +0530, Bharata B Rao wrote:

On Fri, Jul 17, 2020 at 01:00:26AM -0700, Ram Pai wrote:

quoted

@@ -812,7 +842,7 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 	struct vm_area_struct *vma;
 	int srcu_idx;
 	unsigned long gfn = gpa >> page_shift;
-	int ret;
+	int ret, repeat_count = REPEAT_COUNT;
 
 	if (!(kvm->arch.secure_guest & KVMPPC_SECURE_INIT_START))
 		return H_UNSUPPORTED;

@@ -826,34 +856,44 @@ unsigned long kvmppc_h_svm_page_in(struct kvm *kvm, unsigned long gpa,
 	if (flags & H_PAGE_IN_SHARED)
 		return kvmppc_share_page(kvm, gpa, page_shift);
 
-	ret = H_PARAMETER;
 	srcu_idx = srcu_read_lock(&kvm->srcu);
-	mmap_read_lock(kvm->mm);
 
-	start = gfn_to_hva(kvm, gfn);
-	if (kvm_is_error_hva(start))
-		goto out;
-
-	mutex_lock(&kvm->arch.uvmem_lock);
 	/* Fail the page-in request of an already paged-in page */
-	if (kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL))
-		goto out_unlock;
+	mutex_lock(&kvm->arch.uvmem_lock);
+	ret = kvmppc_gfn_is_uvmem_pfn(gfn, kvm, NULL);
+	mutex_unlock(&kvm->arch.uvmem_lock);

Same comment as for the prev patch. I don't think you can release
the lock here.

quoted

+	if (ret) {
+		srcu_read_unlock(&kvm->srcu, srcu_idx);
+		return H_PARAMETER;
+	}
 
-	end = start + (1UL << page_shift);
-	vma = find_vma_intersection(kvm->mm, start, end);
-	if (!vma || vma->vm_start > start || vma->vm_end < end)
-		goto out_unlock;
+	do {
+		ret = H_PARAMETER;
+		mmap_read_lock(kvm->mm);
 
-	if (kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift,
-				true))
-		goto out_unlock;
+		start = gfn_to_hva(kvm, gfn);
+		if (kvm_is_error_hva(start)) {
+			mmap_read_unlock(kvm->mm);
+			break;
+		}
 
-	ret = H_SUCCESS;
+		end = start + (1UL << page_shift);
+		vma = find_vma_intersection(kvm->mm, start, end);
+		if (!vma || vma->vm_start > start || vma->vm_end < end) {
+			mmap_read_unlock(kvm->mm);
+			break;
+		}
+
+		mutex_lock(&kvm->arch.uvmem_lock);
+		ret = kvmppc_svm_migrate_page(vma, start, end, gpa, kvm, page_shift, true);
+		mutex_unlock(&kvm->arch.uvmem_lock);
+
+		mmap_read_unlock(kvm->mm);
+	} while (ret == -2 && repeat_count--);
+
+	if (ret == -2)
+		ret = H_BUSY;
 
-out_unlock:
-	mutex_unlock(&kvm->arch.uvmem_lock);
-out:
-	mmap_read_unlock(kvm->mm);
 	srcu_read_unlock(&kvm->srcu, srcu_idx);
 	return ret;
 }
-- 
1.8.3.1

-- 
Ram Pai