[PATCH 08/46] hugetlb: add HugeTLB HGM enablement helpers

[James Houghton]

hugetlb_hgm_eligible indicates that a VMA is eligible to have HGM
explicitly enabled via MADV_SPLIT, and hugetlb_hgm_enabled indicates
that HGM has been enabled.

Signed-off-by: James Houghton <jthoughton@xxxxxxxxxx>
---
 include/linux/hugetlb.h | 14 ++++++++++++++
 mm/hugetlb.c            | 23 +++++++++++++++++++++++
 2 files changed, 37 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index aa49fd8cb47c..8713d9c4f86c 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -1207,6 +1207,20 @@ static inline void hugetlb_unregister_node(struct node *node)
 }
 #endif	/* CONFIG_HUGETLB_PAGE */
 
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+bool hugetlb_hgm_enabled(struct vm_area_struct *vma);
+bool hugetlb_hgm_eligible(struct vm_area_struct *vma);
+#else
+static inline bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
+{
+	return false;
+}
+static inline bool hugetlb_hgm_eligible(struct vm_area_struct *vma)
+{
+	return false;
+}
+#endif
+
 static inline spinlock_t *huge_pte_lock(struct hstate *h,
 					struct mm_struct *mm, pte_t *pte)
 {
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 2f86fedef283..d27fe05d5ef6 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -6966,6 +6966,10 @@ static bool pmd_sharing_possible(struct vm_area_struct *vma)
 #ifdef CONFIG_USERFAULTFD
 	if (uffd_disable_huge_pmd_share(vma))
 		return false;
+#endif
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+	if (hugetlb_hgm_enabled(vma))
+		return false;
 #endif
 	/*
 	 * Only shared VMAs can share PMDs.
@@ -7229,6 +7233,25 @@ __weak unsigned long hugetlb_mask_last_page(struct hstate *h)
 
 #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
 
+#ifdef CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING
+bool hugetlb_hgm_eligible(struct vm_area_struct *vma)
+{
+	/*
+	 * All shared VMAs may have HGM.
+	 *
+	 * HGM requires using the VMA lock, which only exists for shared VMAs.
+	 * To make HGM work for private VMAs, we would need to use another
+	 * scheme to prevent collapsing/splitting from invalidating other
+	 * threads' page table walks.
+	 */
+	return vma && (vma->vm_flags & VM_MAYSHARE);
+}
+bool hugetlb_hgm_enabled(struct vm_area_struct *vma)
+{
+	return vma && (vma->vm_flags & VM_HUGETLB_HGM);
+}
+#endif /* CONFIG_HUGETLB_HIGH_GRANULARITY_MAPPING */
+
 /*
  * These functions are overwritable if your architecture needs its own
  * behavior.
-- 
2.39.0.314.g84b9a713c41-goog