v4.19.13 snapshot.
diff --git a/arch/x86/hyperv/nested.c b/arch/x86/hyperv/nested.c
new file mode 100644
index 0000000..b8e60cc
--- /dev/null
+++ b/arch/x86/hyperv/nested.c
@@ -0,0 +1,56 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Hyper-V nested virtualization code.
+ *
+ * Copyright (C) 2018, Microsoft, Inc.
+ *
+ * Author : Lan Tianyu <Tianyu.Lan@microsoft.com>
+ */
+
+
+#include <linux/types.h>
+#include <asm/hyperv-tlfs.h>
+#include <asm/mshyperv.h>
+#include <asm/tlbflush.h>
+
+#include <asm/trace/hyperv.h>
+
+int hyperv_flush_guest_mapping(u64 as)
+{
+ struct hv_guest_mapping_flush **flush_pcpu;
+ struct hv_guest_mapping_flush *flush;
+ u64 status;
+ unsigned long flags;
+ int ret = -ENOTSUPP;
+
+ if (!hv_hypercall_pg)
+ goto fault;
+
+ local_irq_save(flags);
+
+ flush_pcpu = (struct hv_guest_mapping_flush **)
+ this_cpu_ptr(hyperv_pcpu_input_arg);
+
+ flush = *flush_pcpu;
+
+ if (unlikely(!flush)) {
+ local_irq_restore(flags);
+ goto fault;
+ }
+
+ flush->address_space = as;
+ flush->flags = 0;
+
+ status = hv_do_hypercall(HVCALL_FLUSH_GUEST_PHYSICAL_ADDRESS_SPACE,
+ flush, NULL);
+ local_irq_restore(flags);
+
+ if (!(status & HV_HYPERCALL_RESULT_MASK))
+ ret = 0;
+
+fault:
+ trace_hyperv_nested_flush_guest_mapping(as, ret);
+ return ret;
+}
+EXPORT_SYMBOL_GPL(hyperv_flush_guest_mapping);