Subject: [PATCH v2 01/13] powerpc/mm: Add DEBUG_VM WARN for pmd_clear

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 19 Aug 2020 18:30:55 +0530

With the hash page table, the kernel should not use pmd_clear for clearing
huge pte entries. Add a DEBUG_VM WARN to catch the wrong usage.

Signed-off-by: Aneesh Kumar K.V <[email-masked]>
---
 arch/powerpc/include/asm/book3s/64/pgtable.h | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/powerpc/include/asm/book3s/64/pgtable.h b/arch/powerpc/include/asm/book3s/64/pgtable.h
index 6de56c3b33c4..079211968987 100644
--- a/arch/powerpc/include/asm/book3s/64/pgtable.h
+++ b/arch/powerpc/include/asm/book3s/64/pgtable.h
@@ -868,6 +868,13 @@ static inline bool pte_ci(pte_t pte)
 
 static inline void pmd_clear(pmd_t *pmdp)
 {
+	if (IS_ENABLED(CONFIG_DEBUG_VM) && !radix_enabled()) {
+		/*
+		 * Don't use this if we can possibly have a hash page table
+		 * entry mapping this.
+		 */
+		WARN_ON((pmd_val(*pmdp) & (H_PAGE_HASHPTE | _PAGE_PTE)) == (H_PAGE_HASHPTE | _PAGE_PTE));
+	}
 	*pmdp = __pmd(0);
 }
 
@@ -916,6 +923,13 @@ static inline int pmd_bad(pmd_t pmd)
 
 static inline void pud_clear(pud_t *pudp)
 {
+	if (IS_ENABLED(CONFIG_DEBUG_VM) && !radix_enabled()) {
+		/*
+		 * Don't use this if we can possibly have a hash page table
+		 * entry mapping this.
+		 */
+		WARN_ON((pud_val(*pudp) & (H_PAGE_HASHPTE | _PAGE_PTE)) == (H_PAGE_HASHPTE | _PAGE_PTE));
+	}
 	*pudp = __pud(0);
 }
 
-- 
2.26.2