Add support for sending a pagefault event if userfaultfd is registered.
Only page minor event is currently supported.

Signed-off-by: Nikita Kalyazin <kalyazin@amazon.com>
---
 virt/kvm/guest_memfd.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
index 26b1734b9623..92d3e6b51dc2 100644
--- a/virt/kvm/guest_memfd.c
+++ b/virt/kvm/guest_memfd.c
@@ -4,6 +4,9 @@
 #include <linux/kvm_host.h>
 #include <linux/pagemap.h>
 #include <linux/anon_inodes.h>
+#ifdef CONFIG_KVM_PRIVATE_MEM
+#include <linux/userfaultfd_k.h>
+#endif /* CONFIG_KVM_PRIVATE_MEM */
 
 #include "kvm_mm.h"
 
@@ -380,6 +383,13 @@ static vm_fault_t kvm_gmem_fault(struct vm_fault *vmf)
 		kvm_gmem_mark_prepared(folio);
 	}
 
+	if (userfaultfd_minor(vmf->vma) &&
+	    !(vmf->flags & FAULT_FLAG_NO_USERFAULT_MINOR)) {
+		folio_unlock(folio);
+		filemap_invalidate_unlock_shared(inode->i_mapping);
+		return handle_userfault(vmf, VM_UFFD_MINOR);
+	}
+
 	vmf->page = folio_file_page(folio, vmf->pgoff);
 
 out_folio:
-- 
2.47.1