[RFC v4][PATCH part-2 11/13] mm/dpt: Add decorated page-table remap function

[Alexandre Chartre <alexandre.chartre@oracle.com>]

Add a function to remap an already mapped buffer with a new address in
a decorated page-table: the already mapped buffer is unmapped, and a
new mapping is added for the specified new address.

This is useful to track and remap a buffer which can be freed and
then reallocated.

Signed-off-by: Alexandre Chartre <alexandre.chartre@oracle.com>
---
 arch/x86/include/asm/dpt.h |  1 +
 arch/x86/mm/dpt.c          | 25 +++++++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/arch/x86/include/asm/dpt.h b/arch/x86/include/asm/dpt.h
index fd8c1b84ffe2..3234ba968d80 100644
--- a/arch/x86/include/asm/dpt.h
+++ b/arch/x86/include/asm/dpt.h
@@ -57,6 +57,7 @@ extern int dpt_map_range(struct dpt *dpt, void *ptr, size_t size,
 			 enum page_table_level level);
 extern int dpt_map(struct dpt *dpt, void *ptr, unsigned long size);
 extern void dpt_unmap(struct dpt *dpt, void *ptr);
+extern int dpt_remap(struct dpt *dpt, void **mapping, void *ptr, size_t size);
 
 static inline int dpt_map_module(struct dpt *dpt, char *module_name)
 {
diff --git a/arch/x86/mm/dpt.c b/arch/x86/mm/dpt.c
index adc59f9ed876..9517e3081716 100644
--- a/arch/x86/mm/dpt.c
+++ b/arch/x86/mm/dpt.c
@@ -809,6 +809,31 @@ int dpt_map_percpu(struct dpt *dpt, void *percpu_ptr, size_t size)
 }
 EXPORT_SYMBOL(dpt_map_percpu);
 
+int dpt_remap(struct dpt *dpt, void **current_ptrp, void *new_ptr, size_t size)
+{
+	void *current_ptr = *current_ptrp;
+	int err;
+
+	if (current_ptr == new_ptr) {
+		/* no change, already mapped */
+		return 0;
+	}
+
+	if (current_ptr) {
+		dpt_unmap(dpt, current_ptr);
+		*current_ptrp = NULL;
+	}
+
+	err = dpt_map(dpt, new_ptr, size);
+	if (err)
+		return err;
+
+	*current_ptrp = new_ptr;
+
+	return 0;
+}
+EXPORT_SYMBOL(dpt_remap);
+
 /*
  * dpt_create - allocate a page-table and create a corresponding
  * decorated page-table. The page-table is allocated and aligned
-- 
2.18.2