On Mon, 2023-12-11 at 11:26 +0100, Alexander Potapenko wrote:

quoted

+static inline void *arch_kmsan_get_meta_or_null(void *addr, bool
is_origin)
+{
+       if (addr >= (void *)&S390_lowcore &&
+           addr < (void *)(&S390_lowcore + 1)) {
+               /*
+                * Different lowcores accessed via S390_lowcore are
described
+                * by the same struct page. Resolve the prefix
manually in
+                * order to get a distinct struct page.
+                */
+               addr += (void *)lowcore_ptr[raw_smp_processor_id()]
-
+                       (void *)&S390_lowcore;
+               return kmsan_get_metadata(addr, is_origin);
+       }
+       return NULL;
+}

Is there a possibility for infinite recursion here? E.g. can
`lowcore_ptr[raw_smp_processor_id()]` point somewhere in between
`(void *)&S390_lowcore` and `(void *)(&S390_lowcore + 1))`?

No, it's allocated with __get_free_pages() or memblock_alloc_low().
But since this question came up, I should probably add a check and
a WARN_ON_ONCE() here.