[PATCH 19/21] KVM: guest_memfd: add API to undo kvm_gmem_get_uninit_pfn

[Paolo Bonzini]

In order to be able to redo kvm_gmem_get_uninit_pfn, a hole must be punched
into the filemap, thus allowing FGP_CREAT_ONLY to succeed again.  This will
be used whenever an operation that follows kvm_gmem_get_uninit_pfn fails.

Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 include/linux/kvm_host.h |  7 +++++++
 virt/kvm/guest_memfd.c   | 28 ++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 03bf616b7308..192c58116220 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -2436,6 +2436,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 		     gfn_t gfn, kvm_pfn_t *pfn, int *max_order);
 int kvm_gmem_get_uninit_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 		            gfn_t gfn, kvm_pfn_t *pfn, int *max_order);
+int kvm_gmem_undo_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
+			  gfn_t gfn, int order);
 #else
 static inline int kvm_gmem_get_pfn(struct kvm *kvm,
 				   struct kvm_memory_slot *slot, gfn_t gfn,
@@ -2452,6 +2454,11 @@ static inline int kvm_gmem_get_uninit_pfn(struct kvm *kvm,
 	KVM_BUG_ON(1, kvm);
 	return -EIO;
 }
+
+static inline int kvm_gmem_undo_get_pfn(struct kvm *kvm,
+				        struct kvm_memory_slot *slot, gfn_t gfn,
+				        int order)
+{}
 #endif /* CONFIG_KVM_PRIVATE_MEM */
 
 #ifdef CONFIG_HAVE_KVM_GMEM_PREPARE
diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 7ec7afafc960..535ef1aa34fb 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -590,3 +590,31 @@ int kvm_gmem_get_uninit_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
 	return __kvm_gmem_get_pfn(kvm, slot, gfn, pfn, max_order, false);
 }
 EXPORT_SYMBOL_GPL(kvm_gmem_get_uninit_pfn);
+
+int kvm_gmem_undo_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot,
+		          gfn_t gfn, int order)
+{
+	pgoff_t index = gfn - slot->base_gfn + slot->gmem.pgoff;
+	struct kvm_gmem *gmem;
+	struct file *file;
+	int r;
+
+	file = kvm_gmem_get_file(slot);
+	if (!file)
+		return -EFAULT;
+
+	gmem = file->private_data;
+
+	if (WARN_ON_ONCE(xa_load(&gmem->bindings, index) != slot)) {
+		r = -EIO;
+		goto out_fput;
+	}
+
+	r = kvm_gmem_punch_hole(file_inode(file), index << PAGE_SHIFT, PAGE_SHIFT << order);
+
+out_fput:
+	fput(file);
+
+	return r;
+}
+EXPORT_SYMBOL_GPL(kvm_gmem_undo_get_pfn);
-- 
2.39.0