mm/hugetlb: enforce that PMD PT sharing has split PMD PT locks

Sharing page tables between processes but falling back to per-MM page
table locks cannot possibly work.

So, let's make sure that we do have split PMD locks by adding a new
Kconfig option and letting that depend on CONFIG_SPLIT_PMD_PTLOCKS.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: David Hildenbrand <[email protected]>
Acked-by: Mike Rapoport (Microsoft) <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Christian Brauner <[email protected]>
Cc: Christophe Leroy <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: "H. Peter Anvin" <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Juergen Gross <[email protected]>
Cc: Michael Ellerman <[email protected]>
Cc: Muchun Song <[email protected]>
Cc: "Naveen N. Rao" <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oscar Salvador <[email protected]>
Cc: Peter Xu <[email protected]>
Cc: Russell King <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: davidhildenbrand

fs/Kconfig

@@ -288,6 +288,10 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP
 	depends on ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP
 	depends on SPARSEMEM_VMEMMAP
 
+config HUGETLB_PMD_PAGE_TABLE_SHARING
+	def_bool HUGETLB_PAGE
+	depends on ARCH_WANT_HUGE_PMD_SHARE && SPLIT_PMD_PTLOCKS
+
 config ARCH_HAS_GIGANTIC_PAGE
 	bool
 

include/linux/hugetlb.h

@@ -1251,7 +1251,7 @@ static inline __init void hugetlb_cma_reserve(int order)
 }
 #endif
 
-#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
+#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
 static inline bool hugetlb_pmd_shared(pte_t *pte)
 {
 	return page_count(virt_to_page(pte)) > 1;
@@ -1287,8 +1287,7 @@ bool __vma_private_lock(struct vm_area_struct *vma);
 static inline pte_t *
 hugetlb_walk(struct vm_area_struct *vma, unsigned long addr, unsigned long sz)
 {
-#if defined(CONFIG_HUGETLB_PAGE) && \
-	defined(CONFIG_ARCH_WANT_HUGE_PMD_SHARE) && defined(CONFIG_LOCKDEP)
+#if defined(CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING) && defined(CONFIG_LOCKDEP)
 	struct hugetlb_vma_lock *vma_lock = vma->vm_private_data;
 
 	/*

mm/hugetlb.c

@@ -7211,7 +7211,7 @@ long hugetlb_unreserve_pages(struct inode *inode, long start, long end,
 	return 0;
 }
 
-#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
+#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
 static unsigned long page_table_shareable(struct vm_area_struct *svma,
 				struct vm_area_struct *vma,
 				unsigned long addr, pgoff_t idx)
@@ -7373,7 +7373,7 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma,
 	return 1;
 }
 
-#else /* !CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
+#else /* !CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */
 
 pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
 		      unsigned long addr, pud_t *pud)
@@ -7396,7 +7396,7 @@ bool want_pmd_share(struct vm_area_struct *vma, unsigned long addr)
 {
 	return false;
 }
-#endif /* CONFIG_ARCH_WANT_HUGE_PMD_SHARE */
+#endif /* CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING */
 
 #ifdef CONFIG_ARCH_WANT_GENERAL_HUGETLB
 pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_area_struct *vma,
@@ -7494,7 +7494,7 @@ unsigned long hugetlb_mask_last_page(struct hstate *h)
 /* See description above.  Architectures can provide their own version. */
 __weak unsigned long hugetlb_mask_last_page(struct hstate *h)
 {
-#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
+#ifdef CONFIG_HUGETLB_PMD_PAGE_TABLE_SHARING
 	if (huge_page_size(h) == PMD_SIZE)
 		return PUD_SIZE - PMD_SIZE;
 #endif