On 2/10/25 5:32 PM, Jan Beulich wrote:
On 07.02.2025 14:13, Oleksii Kurochko wrote:
--- a/xen/arch/riscv/pt.c
+++ b/xen/arch/riscv/pt.c
@@ -185,6 +185,57 @@ static int pt_next_level(bool alloc_tbl, pte_t **table,
unsigned int offset)
return XEN_TABLE_NORMAL;
}
+/*
+ * _pt_walk() performs software page table walking and returns the pte_t of
+ * a leaf node or the leaf-most not-present pte_t if no leaf node is found
+ * for further analysis.
+ * Additionally, _pt_walk() returns the level of the found pte.
That's optional, which I think wants expressing here.
+ */
+static pte_t *_pt_walk(vaddr_t va, unsigned int *pte_level)
+{
+ const mfn_t root = get_root_page();
+ unsigned int level;
+ pte_t *table;
+
+ DECLARE_OFFSETS(offsets, va);
+
+ table = map_table(root);
This mapping operation doesn't look to have a counterpart. Aiui ...
+ /*
+ * Find `table` of an entry which corresponds to `va` by iterating for each
+ * page level and checking if the entry points to a next page table or
+ * to a page.
+ *
+ * Two cases are possible:
+ * - ret == XEN_TABLE_SUPER_PAGE means that the entry was found;
+ * (Despite the name) XEN_TABLE_SUPER_PAGE also covers 4K mappings. If
+ * pt_next_level() is called for page table level 0, it results in the
+ * entry being a pointer to a leaf node, thereby returning
+ * XEN_TABLE_SUPER_PAGE, despite of the fact this leaf covers 4k mapping.
+ * - ret == XEN_TABLE_MAP_NONE means that requested `va` wasn't actually
+ * mapped.
+ */
+ for ( level = HYP_PT_ROOT_LEVEL; ; --level )
+ {
+ int ret = pt_next_level(false, &table, offsets[level]);
... the mapping may be replaced here, but a new mapping will then still
be held by this function and ...
+ if ( ret == XEN_TABLE_MAP_NONE || ret == XEN_TABLE_SUPER_PAGE )
+ break;
+
+ ASSERT(level);
+ }
+
+ if ( pte_level )
+ *pte_level = level;
+
+ return table + offsets[level];
+}
... the final one then be transferred to the caller.
+pte_t pt_walk(vaddr_t va, unsigned int *pte_level)
+{
+ return *_pt_walk(va, pte_level);
+}
Hence aiui there needs to be an unmap operation here.
As _pt_walk() returns page table entry, it is needed to transform entry to
table.
Do we have any function in Xen for that?
Or the best I can do is:
pte_t *table = *_pt_walk(va, pte_level) -
TABLE_OFFSET(pt_linear_offset(*pte_level, va)
(of course, it is needed to check if pte_level isn't null and do some extra
actions if it is NULL)
As an option, as all page tables are PAGE_SIZE aligned, we could use
PAGE_OFFSET():
pte_t *entry = _pt_walk(va, pte_level);
pte_t *table = PAGE_OFFSET(entry);
~ Oleksii
