[PATCH V3 2/3] arm64/mm/hotplug: Enable MEM_OFFLINE event handling

[Anshuman Khandual]

This enables MEM_OFFLINE memory event handling. It will help intercept any
possible error condition such as if boot memory some how still got offlined
even after an explicit notifier failure, potentially by a future change in
generic hot plug framework. This would help detect such scenarios and help
debug further.

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Will Deacon <will at kernel.com>
Cc: Mark Rutland <mark.rutland at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Steve Capper <steve.capper at arm.com>
Cc: Mark Brown <broonie at kernel.org>
Cc: linux-arm-kernel at lists.infradead.org
Cc: linux-kernel at vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual at arm.com>
---
 arch/arm64/mm/mmu.c | 37 ++++++++++++++++++++++++++++++++-----
 1 file changed, 32 insertions(+), 5 deletions(-)

diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index df3b7415b128..6b171bd88bcf 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -1482,13 +1482,40 @@ static int prevent_bootmem_remove_notifier(struct notifier_block *nb,
 	unsigned long end_pfn = arg->start_pfn + arg->nr_pages;
 	unsigned long pfn = arg->start_pfn;
 
-	if (action != MEM_GOING_OFFLINE)
+	if ((action != MEM_GOING_OFFLINE) && (action != MEM_OFFLINE))
 		return NOTIFY_OK;
 
-	for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
-		ms = __pfn_to_section(pfn);
-		if (early_section(ms))
-			return NOTIFY_BAD;
+	if (action == MEM_GOING_OFFLINE) {
+		for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+			ms = __pfn_to_section(pfn);
+			if (early_section(ms)) {
+				pr_warn("Boot memory offlining attempted\n");
+				return NOTIFY_BAD;
+			}
+		}
+	} else if (action == MEM_OFFLINE) {
+		for (; pfn < end_pfn; pfn += PAGES_PER_SECTION) {
+			ms = __pfn_to_section(pfn);
+			if (early_section(ms)) {
+
+				/*
+				 * This should have never happened. Boot memory
+				 * offlining should have been prevented by this
+				 * very notifier. Probably some memory removal
+				 * procedure might have changed which would then
+				 * require further debug.
+				 */
+				pr_err("Boot memory offlined\n");
+
+				/*
+				 * Core memory hotplug does not process a return
+				 * code from the notifier for MEM_OFFLINE event.
+				 * Error condition has been reported. Report as
+				 * ignored.
+				 */
+				return NOTIFY_DONE;
+			}
+		}
 	}
 	return NOTIFY_OK;
 }
-- 
2.20.1