[PATCH v2 06/20] hugetlb_vmemmap: Allow architectures to dynamically disallow HVO

[James Houghton <jthoughton@google.com>]

For arm64, only some platforms support HVO. Add an arch hook to prevent
HVO from taking affect if the architecture lacks support.

It may be the case that arch_supports_hugetlb_vmemmap_optimization()
returns false at first but eventually returns true. This is the case on
arm64. When this happens, bootmem hugepages won't be immediately HVOed,
but they will be optimized in prep_and_add_bootmem_folios().

Signed-off-by: James Houghton <jthoughton@google.com>
---
 include/asm-generic/hugetlb.h |  7 +++++++
 mm/hugetlb_vmemmap.c          | 12 ++++++++++++
 2 files changed, 19 insertions(+)

diff --git a/include/asm-generic/hugetlb.h b/include/asm-generic/hugetlb.h
index 635c41cc3479..8d24075d53d4 100644
--- a/include/asm-generic/hugetlb.h
+++ b/include/asm-generic/hugetlb.h
@@ -128,4 +128,11 @@ static inline bool gigantic_page_runtime_supported(void)
 }
 #endif /* __HAVE_ARCH_GIGANTIC_PAGE_RUNTIME_SUPPORTED */
 
+#ifndef __HAVE_ARCH_HVO_SUPPORTED
+static inline bool arch_hugetlb_vmemmap_optimization_supported(void)
+{
+	return IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP);
+}
+#endif /* __HAVE_ARCH_HVO_SUPPORTED */
+
 #endif /* _ASM_GENERIC_HUGETLB_H */
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index 3fdb1e4ce1a1..8596a462fee6 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -16,6 +16,7 @@
 #include <linux/pagewalk.h>
 #include <linux/pgalloc.h>
 #include <linux/vmemmap-optimization.h>
+#include <linux/hugetlb.h>
 
 #include <asm/tlbflush.h>
 #include "hugetlb_vmemmap.h"
@@ -529,6 +530,9 @@ static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *
 	if (!READ_ONCE(vmemmap_optimize_enabled))
 		return false;
 
+	if (!arch_hugetlb_vmemmap_optimization_supported())
+		return false;
+
 	if (!hugetlb_vmemmap_optimizable(h))
 		return false;
 
@@ -731,6 +735,14 @@ void __init hugetlb_vmemmap_optimize_bootmem_page(unsigned long pfn, unsigned in
 	if (!READ_ONCE(vmemmap_optimize_enabled))
 		return;
 
+	/*
+	 * Architectures may return false here but true by the time
+	 * hugetlb_init() is called. In this case, although the folios will
+	 * not be pre-HVOed, they will be optimized in hugetlb_init().
+	 */
+	if (!arch_hugetlb_vmemmap_optimization_supported())
+		return;
+
 	section_set_compound_order_range(pfn, 1UL << order, order);
 }
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog