[PATCH v1 1/6] xen/riscv: add destroy_xen_mappings() to remove mappings in Xen page tables

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

Introduce the destroy_xen_mappings() function, which removes page
mappings in Xen's page tables between a start address s and an end
address e.
The function ensures that both s and e are page-aligned
and verifies that the start address is less than or equal to the end
address before calling pt_update() to invalidate the mappings.
The pt_update() function is called with INVALID_MFN and PTE_VALID=0
in the flags, which tell pt_update() to remove mapping. No additional
ASSERT() is required to check these arguments, as they are hardcoded in
the call to pt_update() within destroy_xen_mappings().

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
 xen/arch/riscv/mm.c | 6 ------
 xen/arch/riscv/pt.c | 8 ++++++++
 2 files changed, 8 insertions(+), 6 deletions(-)

diff --git a/xen/arch/riscv/mm.c b/xen/arch/riscv/mm.c
index 9359dc7f33..f2bf279bac 100644
--- a/xen/arch/riscv/mm.c
+++ b/xen/arch/riscv/mm.c
@@ -360,12 +360,6 @@ int xenmem_add_to_physmap_one(struct domain *d, unsigned 
int space,
     return 0;
 }
 
-int destroy_xen_mappings(unsigned long s, unsigned long e)
-{
-    BUG_ON("unimplemented");
-    return -1;
-}
-
 void share_xen_page_with_guest(struct page_info *page, struct domain *d,
                                enum XENSHARE_flags flags)
 {
diff --git a/xen/arch/riscv/pt.c b/xen/arch/riscv/pt.c
index d62aceb36c..8d35ef5ca8 100644
--- a/xen/arch/riscv/pt.c
+++ b/xen/arch/riscv/pt.c
@@ -421,6 +421,14 @@ int map_pages_to_xen(unsigned long virt,
     return pt_update(virt, mfn, nr_mfns, flags);
 }
 
+int destroy_xen_mappings(unsigned long s, unsigned long e)
+{
+    ASSERT(IS_ALIGNED(s, PAGE_SIZE));
+    ASSERT(IS_ALIGNED(e, PAGE_SIZE));
+    ASSERT(s <= e);
+    return pt_update(s, INVALID_MFN, PFN_DOWN(e - s), 0);
+}
+
 int __init populate_pt_range(unsigned long virt, unsigned long nr_mfns)
 {
     return pt_update(virt, INVALID_MFN, nr_mfns, PTE_POPULATE);
-- 
2.47.0