On 12/8/25 5:52 PM, Jan Beulich wrote:
On 24.11.2025 13:33, Oleksii Kurochko wrote:
@@ -28,6 +36,77 @@ unsigned char get_max_supported_mode(void)
return max_gstage_mode.mode;
}
+static inline unsigned int calc_offset(const struct p2m_domain *p2m,
+ const unsigned int lvl,
+ const paddr_t gpa)
+{
+ unsigned int off = (gpa >> P2M_GFN_LEVEL_SHIFT(lvl)) &
+ P2M_TABLE_OFFSET(p2m, lvl);
+
+ /*
+ * For P2M_ROOT_LEVEL, `offset` ranges from 0 to 2047, since the root
+ * page table spans 4 consecutive 4KB pages.
+ * We want to return an index within one of these 4 pages.
+ * The specific page to use is determined by `p2m_get_root_pointer()`.
+ *
+ * Example: if `offset == 512`:
+ * - A single 4KB page holds 512 entries.
+ * - Therefore, entry 512 corresponds to index 0 of the second page.
+ *
+ * At all other levels, only one page is allocated, and `offset` is
+ * always in the range 0 to 511, since the VPN is 9 bits long.
+ */
+ return off & (PAGETABLE_ENTRIES - 1);
+}
+
+#define P2M_MAX_ROOT_LEVEL 5
+
+#define P2M_BUILD_LEVEL_OFFSETS(p2m, var, addr) \
+ unsigned int var[P2M_MAX_ROOT_LEVEL] = {-1}; \
What use is this initializer? Slot 0 ...
I wanted a way to detect if something mistakenly tries to access an
uninitialized
array element, and using -1 would help distinguish whether an element was truly
uninitialized or if calc_offset() simply returned 0. However, you’re right, it
doesn’t work because only Slot 0 is initialized with -1. So...
+ BUG_ON(P2M_ROOT_LEVEL(p2m) >= P2M_MAX_ROOT_LEVEL); \
+ for ( unsigned int i = 0; i <= P2M_ROOT_LEVEL(p2m); i++ ) \
+ var[i] = calc_offset(p2m, i, addr);
... is guaranteed to be written to, afaics. With this simplified (or an
explanation given for why it is needed)
... I will just drop an initializer and let var[] to be initialized with 0s.
Acked-by: Jan Beulich <[email protected]>
Thanks.
~ Oleksii
