The patch titled Subject: s390: fix HugeTLB vmemmap optimization crash has been added to the -mm mm-hotfixes-unstable branch. Its filename is s390-fix-hugetlb-vmemmap-optimization-crash.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

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

Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's

*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days

------------------------------------------------------ From: Luiz Capitulino luizcap@redhat.com Subject: s390: fix HugeTLB vmemmap optimization crash Date: Tue, 28 Oct 2025 17:15:33 -0400

A reproducible crash occurs when enabling HugeTLB vmemmap optimization (HVO) on s390. The crash and the proposed fix were worked on an s390 KVM guest running on an older hypervisor, as I don't have access to an LPAR. However, the same issue should occur on bare-metal.

Reproducer (it may take a few runs to trigger):

# sysctl vm.hugetlb_optimize_vmemmap=1 # echo 1 > /proc/sys/vm/nr_hugepages # echo 0 > /proc/sys/vm/nr_hugepages

Crash log:

[ 52.340369] list_del corruption. prev->next should be 000000d382110008, but was 000000d7116d3880. (prev=000000d7116d3910) [ 52.340420] ------------[ cut here ]------------ [ 52.340424] kernel BUG at lib/list_debug.c:62! [ 52.340566] monitor event: 0040 ilc:2 [#1]SMP [ 52.340573] Modules linked in: ctcm fsm qeth ccwgroup zfcp scsi_transport_fc qdio dasd_fba_mod dasd_eckd_mod dasd_mod xfs ghash_s390 prng des_s390 libdes sha3_512_s390 sha3_256_s390 virtio_net virtio_blk net_failover sha_common failover dm_mirror dm_region_hash dm_log dm_mod paes_s390 crypto_engine pkey_cca pkey_ep11 zcrypt pkey_pckmo pkey aes_s390 [ 52.340606] CPU: 1 UID: 0 PID: 1672 Comm: root-rep2 Kdump: loaded Not tainted 6.18.0-rc3 #1 NONE [ 52.340610] Hardware name: IBM 3931 LA1 400 (KVM/Linux) [ 52.340611] Krnl PSW : 0704c00180000000 0000015710cda7fe (__list_del_entry_valid_or_report+0xfe/0x128) [ 52.340619] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 CC:0 PM:0 RI:0 EA:3 [ 52.340622] Krnl GPRS: c0000000ffffefff 0000000100000027 000000000000006d 0000000000000000 [ 52.340623] 000000d7116d35d8 000000d7116d35d0 0000000000000002 000000d7116d39b0 [ 52.340625] 000000d7116d3880 000000d7116d3910 000000d7116d3910 000000d382110008 [ 52.340626] 000003ffac1ccd08 000000d7116d39b0 0000015710cda7fa 000000d7116d37d0 [ 52.340632] Krnl Code: 0000015710cda7ee: c020003e496f larl %r2,00000157114a3acc 0000015710cda7f4: c0e5ffd5280e brasl %r14,000001571077f810 #0000015710cda7fa: af000000 mc 0,0 >0000015710cda7fe: b9040029 lgr %r2,%r9 0000015710cda802: c0e5ffe5e193 brasl %r14,0000015710996b28 0000015710cda808: e34090080004 lg %r4,8(%r9) 0000015710cda80e: b9040059 lgr %r5,%r9 0000015710cda812: b9040038 lgr %r3,%r8 [ 52.340643] Call Trace: [ 52.340645] [<0000015710cda7fe>] __list_del_entry_valid_or_report+0xfe/0x128 [ 52.340649] ([<0000015710cda7fa>] __list_del_entry_valid_or_report+0xfa/0x128) [ 52.340652] [<0000015710a30b2e>] hugetlb_vmemmap_restore_folios+0x96/0x138 [ 52.340655] [<0000015710a268ac>] update_and_free_pages_bulk+0x64/0x150 [ 52.340659] [<0000015710a26f8a>] set_max_huge_pages+0x4ca/0x6f0 [ 52.340662] [<0000015710a273ba>] hugetlb_sysctl_handler_common+0xea/0x120 [ 52.340665] [<0000015710a27484>] hugetlb_sysctl_handler+0x44/0x50 [ 52.340667] [<0000015710b53ffa>] proc_sys_call_handler+0x17a/0x280 [ 52.340672] [<0000015710a90968>] vfs_write+0x2c8/0x3a0 [ 52.340676] [<0000015710a90bd2>] ksys_write+0x72/0x100 [ 52.340679] [<00000157111483a8>] __do_syscall+0x150/0x318 [ 52.340682] [<0000015711153a5e>] system_call+0x6e/0x90 [ 52.340684] Last Breaking-Event-Address: [ 52.340684] [<000001571077f85c>] _printk+0x4c/0x58 [ 52.340690] Kernel panic - not syncing: Fatal exception: panic_on_oops

This issue was introduced by commit f13b83fdd996 ("hugetlb: batch TLB flushes when freeing vmemmap"). Before that change, the HVO implementation called flush_tlb_kernel_range() each time a vmemmap PMD split and remapping was performed. The mentioned commit changed this to issue a few flush_tlb_all() calls after performing all remappings.

However, on s390, flush_tlb_kernel_range() expands to __tlb_flush_kernel() while flush_tlb_all() is not implemented. As a result, we went from flushing the TLB for every remapping to no flushing at all.

This commit fixes this by implementing flush_tlb_all() on s390 as an alias to __tlb_flush_global(). This should cause a flush on all TLB entries on all CPUs as expected by the flush_tlb_all() semantics.

Link: https://lkml.kernel.org/r/20251028211533.47694-1-luizcap@redhat.com Fixes: f13b83fdd996 ("hugetlb: batch TLB flushes when freeing vmemmap") Signed-off-by: Luiz Capitulino luizcap@redhat.com Cc: Alexander Gordeev agordeev@linux.ibm.com Cc: "Aneesh Kumar K.V" aneesh.kumar@kernel.org Cc: Christian Borntraeger borntraeger@linux.ibm.com Cc: David Hildenbrand david@redhat.com Cc: Gerald Schaefer gerald.schaefer@linux.ibm.com Cc: Heiko Carstens hca@linux.ibm.com Cc: Joao Martins joao.m.martins@oracle.com Cc: Mike Kravetz mike.kravetz@oracle.com Cc: Oscar Salvador osalvador@suse.de Cc: Vasily Gorbik gor@linux.ibm.com Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

arch/s390/include/asm/tlbflush.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)

--- a/arch/s390/include/asm/tlbflush.h~s390-fix-hugetlb-vmemmap-optimization-crash +++ a/arch/s390/include/asm/tlbflush.h @@ -103,9 +103,13 @@ static inline void __tlb_flush_mm_lazy(s * flush_tlb_range functions need to do the flush. */ #define flush_tlb() do { } while (0) -#define flush_tlb_all() do { } while (0) #define flush_tlb_page(vma, addr) do { } while (0)

+static inline void flush_tlb_all(void) +{ + __tlb_flush_global(); +} + static inline void flush_tlb_mm(struct mm_struct *mm) { __tlb_flush_mm_lazy(mm); _

Patches currently in -mm which might be from luizcap@redhat.com are

s390-fix-hugetlb-vmemmap-optimization-crash.patch