[PATCH 15/18] hugetlb_vmemmap: Add a way to permanently disable HVO when needed

[James Houghton <jthoughton@google.com>]

hugetlb_vmemmap_optimization_try_disable() is used by callers to
permanently disable HVO if it becomes impossible to use.

If HVO is already actively in use,
hugetlb_vmemmap_optimization_try_disable() returns false to inform the
caller to take appropriate action (e.g., for arm64, not to online an
incompatible late CPU).

Signed-off-by: James Houghton <jthoughton@google.com>
---
 MAINTAINERS                     |  1 +
 include/linux/hugetlb_vmemmap.h | 20 +++++++++++++++++
 mm/hugetlb_vmemmap.c            | 40 +++++++++++++++++++++++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 include/linux/hugetlb_vmemmap.h

diff --git a/MAINTAINERS b/MAINTAINERS
index ff47013ce995..55bd4c09f494 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12013,6 +12013,7 @@ F:	Documentation/mm/hugetlbfs_reserv.rst
 F:	Documentation/mm/vmemmap_dedup.rst
 F:	fs/hugetlbfs/
 F:	include/linux/hugetlb.h
+F:	include/linux/hugetlb_vmemmap.h
 F:	include/trace/events/hugetlbfs.h
 F:	mm/hugetlb.c
 F:	mm/hugetlb_cgroup.c
diff --git a/include/linux/hugetlb_vmemmap.h b/include/linux/hugetlb_vmemmap.h
new file mode 100644
index 000000000000..a671eb4a4ff4
--- /dev/null
+++ b/include/linux/hugetlb_vmemmap.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _LINUX_HUGETLB_VMEMMAP_H
+#define _LINUX_HUGETLB_VMEMMAP_H
+
+#include <linux/types.h>
+
+#ifdef CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP
+
+bool hugetlb_vmemmap_optimization_try_disable(void);
+
+#else /* CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP */
+
+static inline bool hugetlb_vmemmap_optimization_try_disable(void)
+{
+	return true;
+}
+
+#endif
+
+#endif /* _LINUX_HUGETLB_VMEMMAP_H */
diff --git a/mm/hugetlb_vmemmap.c b/mm/hugetlb_vmemmap.c
index a490a34998d9..7e7f8579cc2a 100644
--- a/mm/hugetlb_vmemmap.c
+++ b/mm/hugetlb_vmemmap.c
@@ -17,6 +17,7 @@
 #include <linux/pagewalk.h>
 #include <linux/pgalloc.h>
 #include <linux/hugetlb.h>
+#include <linux/hugetlb_vmemmap.h>
 
 #include <asm/tlbflush.h>
 #include "hugetlb_vmemmap_internal.h"
@@ -463,6 +464,39 @@ static int vmemmap_remap_alloc(const struct hstate *h, struct folio *folio,
 	return ret;
 }
 
+enum hugetlb_hvo_status {
+	HVO_INACTIVE = 0,
+	HVO_ACTIVE,
+	HVO_PERMANENTLY_INACTIVE,
+};
+static enum hugetlb_hvo_status hvo_status = HVO_INACTIVE;
+
+static bool hugetlb_hvo_status_try_set(enum hugetlb_hvo_status status)
+{
+	enum hugetlb_hvo_status old;
+
+	old = READ_ONCE(hvo_status);
+
+retry:
+	/* The current setting is what we want. */
+	if (old == status)
+		return true;
+
+	/* The current setting cannot be changed. */
+	if (old != HVO_INACTIVE)
+		return false;
+
+	if (!try_cmpxchg_relaxed(&hvo_status, &old, status))
+		goto retry;
+
+	return true;
+}
+
+bool hugetlb_vmemmap_optimization_try_disable(void)
+{
+	return hugetlb_hvo_status_try_set(HVO_PERMANENTLY_INACTIVE);
+}
+
 static bool vmemmap_optimize_enabled = IS_ENABLED(CONFIG_HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON);
 static int __init hugetlb_vmemmap_optimize_param(char *buf)
 {
@@ -571,6 +605,9 @@ static bool vmemmap_should_optimize_folio(const struct hstate *h, struct folio *
 	if (!hugetlb_vmemmap_optimizable(h))
 		return false;
 
+	if (!hugetlb_hvo_status_try_set(HVO_ACTIVE))
+		return false;
+
 	return true;
 }
 
@@ -809,6 +846,9 @@ static bool vmemmap_should_optimize_bootmem_page(struct huge_bootmem_page *m)
 	    !IS_ALIGNED(psize, pmd_vmemmap_size))
 		return false;
 
+	if (!hugetlb_hvo_status_try_set(HVO_ACTIVE))
+		return false;
+
 	return true;
 }
 
-- 
2.55.0.795.g602f6c329a-goog