[PATCH] mm/arch: Provide pud_pfn() fallback

[peterx]

From: Peter Xu <peterx@xxxxxxxxxx>

The comment in the code explains the reasons.  We took a different approach
comparing to pmd_pfn() by providing a fallback function.

Another option is to provide some lower level config options (compare to
HUGETLB_PAGE or THP) to identify which layer an arch can support for such
huge mappings.  However that can be an overkill.

Cc: Mike Rapoport (IBM) <rppt@xxxxxxxxxx>
Cc: Matthew Wilcox <willy@xxxxxxxxxxxxx>
Reported-by: kernel test robot <lkp@xxxxxxxxx>
Closes: https://lore.kernel.org/oe-kbuild-all/202403231529.HRev1zcD-lkp@xxxxxxxxx/
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
---

Andrew,

If we care about per-commit build errors (and if it is ever feasible to
reorder), we can move this patch to be before the patch "mm/gup: handle
huge pud for follow_pud_mask()" in mm-unstable to unbreak build on that
commit.

Thanks,
---
 arch/riscv/include/asm/pgtable.h    |  1 +
 arch/s390/include/asm/pgtable.h     |  1 +
 arch/sparc/include/asm/pgtable_64.h |  1 +
 arch/x86/include/asm/pgtable.h      |  1 +
 include/linux/pgtable.h             | 10 ++++++++++
 5 files changed, 14 insertions(+)

diff --git a/arch/riscv/include/asm/pgtable.h b/arch/riscv/include/asm/pgtable.h
index 20242402fc11..0ca28cc8e3fa 100644
--- a/arch/riscv/include/asm/pgtable.h
+++ b/arch/riscv/include/asm/pgtable.h
@@ -646,6 +646,7 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 
 #define __pud_to_phys(pud)  (__page_val_to_pfn(pud_val(pud)) << PAGE_SHIFT)
 
+#define pud_pfn pud_pfn
 static inline unsigned long pud_pfn(pud_t pud)
 {
 	return ((__pud_to_phys(pud) & PUD_MASK) >> PAGE_SHIFT);
diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
index 1a71cb19c089..6cbbe473f680 100644
--- a/arch/s390/include/asm/pgtable.h
+++ b/arch/s390/include/asm/pgtable.h
@@ -1414,6 +1414,7 @@ static inline unsigned long pud_deref(pud_t pud)
 	return (unsigned long)__va(pud_val(pud) & origin_mask);
 }
 
+#define pud_pfn pud_pfn
 static inline unsigned long pud_pfn(pud_t pud)
 {
 	return __pa(pud_deref(pud)) >> PAGE_SHIFT;
diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
index 4d1bafaba942..26efc9bb644a 100644
--- a/arch/sparc/include/asm/pgtable_64.h
+++ b/arch/sparc/include/asm/pgtable_64.h
@@ -875,6 +875,7 @@ static inline bool pud_leaf(pud_t pud)
 	return pte_val(pte) & _PAGE_PMD_HUGE;
 }
 
+#define pud_pfn pud_pfn
 static inline unsigned long pud_pfn(pud_t pud)
 {
 	pte_t pte = __pte(pud_val(pud));
diff --git a/arch/x86/include/asm/pgtable.h b/arch/x86/include/asm/pgtable.h
index cefc7a84f7a4..273f7557218c 100644
--- a/arch/x86/include/asm/pgtable.h
+++ b/arch/x86/include/asm/pgtable.h
@@ -234,6 +234,7 @@ static inline unsigned long pmd_pfn(pmd_t pmd)
 	return (pfn & pmd_pfn_mask(pmd)) >> PAGE_SHIFT;
 }
 
+#define pud_pfn pud_pfn
 static inline unsigned long pud_pfn(pud_t pud)
 {
 	phys_addr_t pfn = pud_val(pud);
diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h
index 2a1c044ae467..deae9e50f1a8 100644
--- a/include/linux/pgtable.h
+++ b/include/linux/pgtable.h
@@ -1817,6 +1817,16 @@ typedef unsigned int pgtbl_mod_mask;
 #define pte_leaf_size(x) PAGE_SIZE
 #endif
 
+/*
+ * We always define pmd_pfn for all archs as it's used in lots of generic
+ * code.  Now it happens too for pud_pfn (and can happen for larger
+ * mappings too in the future; we're not there yet).  Instead of defining
+ * it for all archs (like pmd_pfn), provide a fallback.
+ */
+#ifndef pud_pfn
+#define pud_pfn(x) ({ BUILD_BUG(); 0; })
+#endif
+
 /*
  * Some architectures have MMUs that are configurable or selectable at boot
  * time. These lead to variable PTRS_PER_x. For statically allocated arrays it
-- 
2.44.0