Excerpts from Russell King - ARM Linux admin's message of February 2, 2021 9:13 pm:

On Tue, Feb 02, 2021 at 09:05:02PM +1000, Nicholas Piggin wrote:

quoted

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index c02f24400369..d63a5bb6bd0c 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h

@@ -166,6 +166,9 @@ extern struct page *empty_zero_page;
 
 extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 
+#define pud_page(pud)		pmd_page(__pmd(pud_val(pud)))
+#define pud_write(pud)		pmd_write(__pmd(pud_val(pud)))

As there is no PUD, does it really make sense to return a valid
struct page (which will be the PTE page) for pud_page(), which is
several tables above?

There is no PUD on 3-level either, and the pgtable-nopud.h which it uses 
also passes down p4d_page to pud_page, so by convention...

Although in this case at least for my next patch it won't acutally use 
pud_page unless it's a leaf entry so maybe it shouldn't get called
anyway.

Thanks,
Nick