+ mm-fix-huge-page-table-not-free-after-memory-unplug.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: mm: fix huge page table not free after memory unplug
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     mm-fix-huge-page-table-not-free-after-memory-unplug.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-fix-huge-page-table-not-free-after-memory-unplug.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Yuan Liu <yuan1.liu@intel.com>
Subject: mm: fix huge page table not free after memory unplug
Date: Sun, 21 Dec 2025 23:11:17 -0500

Newly plugged memory is marked as prot_sethuge via phys_pmd_init without
setting PG_head.  During memory unplug, free_hugepage_table frees the page
table as 2M, but pagetable_free handles it as 4K.

The following test case of memory unplug for a VM [1], tested in the
environment [2], show that results.

+-----------------------+------+------+
|Check System Memory    |Plug  |Unplug|
|via free -h            |256GB |256GB |
+-----------------------+------+------+
| Free 4K page table    |257GB |5.6GB |
+-----------------------+------+------+
| Free 2M page table    |257GB |1.7GB |
+-----------------------+------+------+

[1] Qemu commands to unhotplug 256G memory for a VM:
    object_add memory-backend-ram,id=hotmem0,size=256G,share=on
    device_add virtio-mem-pci,id=vmem1,memdev=hotmem0,bus=port1
    qom-set vmem1 requested-size 256G (Plug Memory)
    qom-set vmem1 requested-size 0G (Unplug Memory)

[2] Hardware     : Intel Icelake server
    Guest Kernel : v6.19-rc1
    Qemu         : v9.0.0

Launch VM:
    qemu-system-x86_64 -accel kvm -cpu host \
    -drive file=./Centos10_cloud.qcow2,format=qcow2,if=virtio \
    -drive file=./seed.img,format=raw,if=virtio \
    -smp 3,cores=3,threads=1,sockets=1,maxcpus=3 \
    -m 2G,slots=10,maxmem=2052472M \
    -device pcie-root-port,id=port1,bus=pcie.0,slot=1,multifunction=on \
    -device pcie-root-port,id=port2,bus=pcie.0,slot=2 \
    -nographic -machine q35 \
    -nic user,hostfwd=tcp::3000-:22

   Guest kernel auto-onlines newly added memory blocks:
   echo online > /sys/devices/system/memory/auto_online_blocks

Link: https://lkml.kernel.org/r/20251222041117.44865-1-yuan1.liu@intel.com
Fixes: bf9e4e30f353 ("x86/mm: use pagetable_free()")
Signed-off-by: Yuan Liu <yuan1.liu@intel.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Cc: Baolu Lu <baolu.lu@linux.intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Mike Rapoport <rppt@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 arch/x86/mm/init_64.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/mm/init_64.c~mm-fix-huge-page-table-not-free-after-memory-unplug
+++ a/arch/x86/mm/init_64.c
@@ -1028,7 +1028,7 @@ static void __meminit free_pagetable(str
 		free_reserved_pages(page, nr_pages);
 #endif
 	} else {
-		pagetable_free(page_ptdesc(page));
+		__free_pages(page, order);
 	}
 }
 
_

Patches currently in -mm which might be from yuan1.liu@intel.com are

mm-fix-huge-page-table-not-free-after-memory-unplug.patch