[PATCH v20 9/9] firmware: arm_rmm: hotplug: Skip memory added to ZONE_MOVABLE

[Suzuki K Poulose]

If the hotadded memory is in ZONE_MOVABLE, we could allow that to proceed
without the RMM having fine grained tracking, as we won't allocate pages
from there for guest-memfd or kernel allocation

Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: David Hildenbrand (Arm) <david at kernel.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
---
Changes since v19:
 - New patch in v20, keeping this at the tail to allow for the rest of the
   series to proceed, while this patch gets discussed.
---
 drivers/firmware/arm_rmm/rmi.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/firmware/arm_rmm/rmi.c b/drivers/firmware/arm_rmm/rmi.c
index d4d098448e46e..ef0a171ba9677 100644
--- a/drivers/firmware/arm_rmm/rmi.c
+++ b/drivers/firmware/arm_rmm/rmi.c
@@ -1043,6 +1043,18 @@ static int rmi_memory_notifier(struct notifier_block *nb,
 	start = PFN_PHYS(arg->start_pfn);
 	end = PFN_PHYS(arg->start_pfn + arg->nr_pages);
 
+	/*
+	 * If the hotplugged memory region is in ZONE_MOVABLE, neither the
+	 * guest-memfd nor the kernel allocations can come from there. So we are
+	 * fine to skip this.
+	 * For boot time memory, we don't allow this discount, as the
+	 * decision to move boot memory pages to ZONE_MOVABLE is purely
+	 * a kernel choice and the firmware must have decided what it covers.
+	 */
+	if (page_zonenum(pfn_to_page(arg->start_pfn)) == ZONE_MOVABLE &&
+	    page_zonenum(pfn_to_page(arg->start_pfn + arg->nr_pages - 1)) == ZONE_MOVABLE)
+		return NOTIFY_DONE;
+
 	ret = rmi_prepare_memory(start, end);
 
 	return notifier_from_errno(ret);
-- 
2.43.0