This is a note to let you know that I've just added the patch titled

ipc/shm.c: add split function to shm_vm_ops

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: ipc-shm.c-add-split-function-to-shm_vm_ops.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From 3d942ee079b917b24e2a0c5f18d35ac8ec9fee48 Mon Sep 17 00:00:00 2001

From: Mike Kravetz mike.kravetz@oracle.com Date: Wed, 28 Mar 2018 16:01:01 -0700 Subject: ipc/shm.c: add split function to shm_vm_ops

From: Mike Kravetz mike.kravetz@oracle.com

commit 3d942ee079b917b24e2a0c5f18d35ac8ec9fee48 upstream.

If System V shmget/shmat operations are used to create a hugetlbfs backed mapping, it is possible to munmap part of the mapping and split the underlying vma such that it is not huge page aligned. This will untimately result in the following BUG:

kernel BUG at /build/linux-jWa1Fv/linux-4.15.0/mm/hugetlb.c:3310! Oops: Exception in kernel mode, sig: 5 [#1] LE SMP NR_CPUS=2048 NUMA PowerNV Modules linked in: kcm nfc af_alg caif_socket caif phonet fcrypt CPU: 18 PID: 43243 Comm: trinity-subchil Tainted: G C E 4.15.0-10-generic #11-Ubuntu NIP: c00000000036e764 LR: c00000000036ee48 CTR: 0000000000000009 REGS: c000003fbcdcf810 TRAP: 0700 Tainted: G C E (4.15.0-10-generic) MSR: 9000000000029033 <SF,HV,EE,ME,IR,DR,RI,LE> CR: 24002222 XER: 20040000 CFAR: c00000000036ee44 SOFTE: 1 NIP __unmap_hugepage_range+0xa4/0x760 LR __unmap_hugepage_range_final+0x28/0x50 Call Trace: 0x7115e4e00000 (unreliable) __unmap_hugepage_range_final+0x28/0x50 unmap_single_vma+0x11c/0x190 unmap_vmas+0x94/0x140 exit_mmap+0x9c/0x1d0 mmput+0xa8/0x1d0 do_exit+0x360/0xc80 do_group_exit+0x60/0x100 SyS_exit_group+0x24/0x30 system_call+0x58/0x6c ---[ end trace ee88f958a1c62605 ]---

This bug was introduced by commit 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct"). A split function was added to vm_operations_struct to determine if a mapping can be split. This was mostly for device-dax and hugetlbfs mappings which have specific alignment constraints.

Mappings initiated via shmget/shmat have their original vm_ops overwritten with shm_vm_ops. shm_vm_ops functions will call back to the original vm_ops if needed. Add such a split function to shm_vm_ops.

Link: http://lkml.kernel.org/r/20180321161314.7711-1-mike.kravetz@oracle.com Fixes: 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct") Signed-off-by: Mike Kravetz mike.kravetz@oracle.com Reported-by: Laurent Dufour ldufour@linux.vnet.ibm.com Reviewed-by: Laurent Dufour ldufour@linux.vnet.ibm.com Tested-by: Laurent Dufour ldufour@linux.vnet.ibm.com Reviewed-by: Dan Williams dan.j.williams@intel.com Acked-by: Michal Hocko mhocko@suse.com Cc: Davidlohr Bueso dave@stgolabs.net Cc: Manfred Spraul manfred@colorfullife.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Linus Torvalds torvalds@linux-foundation.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- ipc/shm.c | 12 ++++++++++++ 1 file changed, 12 insertions(+)

--- a/ipc/shm.c +++ b/ipc/shm.c @@ -386,6 +386,17 @@ static int shm_fault(struct vm_fault *vm return sfd->vm_ops->fault(vmf); }

+static int shm_split(struct vm_area_struct *vma, unsigned long addr) +{ + struct file *file = vma->vm_file; + struct shm_file_data *sfd = shm_file_data(file); + + if (sfd->vm_ops && sfd->vm_ops->split) + return sfd->vm_ops->split(vma, addr); + + return 0; +} + #ifdef CONFIG_NUMA static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new) { @@ -510,6 +521,7 @@ static const struct vm_operations_struct .open = shm_open, /* callback for a new vm-area open */ .close = shm_close, /* callback for when the vm-area is released */ .fault = shm_fault, + .split = shm_split, #if defined(CONFIG_NUMA) .set_policy = shm_set_policy, .get_policy = shm_get_policy,

Patches currently in stable-queue which might be from mike.kravetz@oracle.com are

queue-4.15/ipc-shm.c-add-split-function-to-shm_vm_ops.patch