[PATCH v2 10/20] hugetlb_vmemmap: Expose whether HVO is enabled to architecture code

[James Houghton <jthoughton@google.com>]

Architectures that select CONFIG_ARCH_WANT_HUGETLB_VMEMMAP_RO_AFTER_INIT
may configure the system at boot depending on whether HVO is enabled,
e.g. arm64 requires all CPUs to support hardware access flag updates
only if HVO is enabled.

Add hugetlb_vmemmap_optimize_enabled() so that they can check. It is
declared before <asm/hugetlb.h> is included, so that it can also be used
from inline helpers there.

It only reflects the hugetlb_free_vmemmap= kernel command line parameter
(and the sysctl, when writable), not whether the architecture supports
HVO.

Signed-off-by: James Houghton <jthoughton@google.com>
---
 include/linux/hugetlb.h |  9 +++++++++
 mm/hugetlb_vmemmap.c    | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index 5029c7241863..1ef73b5da664 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -22,6 +22,15 @@ struct node;
 
 void free_huge_folio(struct folio *folio);
 
+#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+bool hugetlb_vmemmap_optimize_enabled(void);
+#else
+static inline bool hugetlb_vmemmap_optimize_enabled(void)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_HUGETLB_PAGE
 
 #include <linux/pagemap.h>
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index de4148a8aabf..c1c736dd08b9 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -448,6 +448,24 @@ static int __init hugetlb_vmemmap_optimize_param(char *buf)
 }
 early_param("hugetlb_free_vmemmap", hugetlb_vmemmap_optimize_param);
 
+/**
+ * hugetlb_vmemmap_optimize_enabled - whether HVO is enabled
+ *
+ * This only reflects the hugetlb_free_vmemmap= kernel command line parameter
+ * and the vm.hugetlb_optimize_vmemmap sysctl, not whether the architecture
+ * supports HVO (see arch_hugetlb_vmemmap_optimization_supported()).
+ *
+ * The value is final once early parameters have been parsed only if the
+ * architecture selects CONFIG_ARCH_WANT_HUGETLB_VMEMMAP_RO_AFTER_INIT;
+ * otherwise it may change at any time through the sysctl.
+ *
+ * Return: true if HVO is enabled.
+ */
+bool hugetlb_vmemmap_optimize_enabled(void)
+{
+	return READ_ONCE(vmemmap_optimize_enabled);
+}
+
 static int __hugetlb_vmemmap_restore_folio(const struct hstate *h,
 					   struct folio *folio, unsigned long flags)
 {
-- 
2.56.0.rc1.315.gc6ed9934b7-goog