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References: <20230903151328.2981432-1-joel@joelfernandes.org>
In-Reply-To: <20230903151328.2981432-1-joel@joelfernandes.org>
From:   zhenyu zhang <zhenyzha12@gmail.com>
Date:   Mon, 18 Sep 2023 23:35:56 +0800
Message-ID: <CA+bgdggjp-sYfgRHV18vnc53SoHUU4=0bQHUxvSN8LZFchVjtw@mail.gmail.com>
Subject: Re: [PATCH v6 0/7] Optimize mremap during mutual alignment within PMD
To:     joel@joelfernandes.org
Cc:     linux-kernel@vger.kernel.org, linux-kselftest@vger.kernel.org,
        linux-mm@kvack.org, Shuah Khan <shuah@kernel.org>,
        Vlastimil Babka <vbabka@suse.cz>,
        Michal Hocko <mhocko@suse.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Lorenzo Stoakes <lstoakes@gmail.com>,
        Kirill A Shutemov <kirill@shutemov.name>,
        "Liam R. Howlett" <liam.howlett@oracle.com>,
        "Paul E. McKenney" <paulmck@kernel.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Kalesh Singh <kaleshsingh@google.com>,
        Lokesh Gidra <lokeshgidra@google.com>, gshan@redhat.com,
        david@redhat.com
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Precedence: bulk

With 4k guest and 64k host, on aarch64(Ampere's Altra Max CPU) hit Call tra=
ce:
    Steps:
    1) System setup hugepages on host.
       # echo 50 > /proc/sys/vm/nr_hugepages
    2) Mount this hugepage to /mnt/kvm_hugepage.
       # mount -t hugetlbfs -o pagesize=3D524288K none /mnt/kvm_hugepage
    3) HugePages didn't leak when using non-existent mem-path.
       # cd /home/kar/workspace/avocado-vt/virttest; mkdir -p /mnt/tmp
    4) Run memory heavy stress inside guest.
       # /usr/libexec/qemu-kvm \
         ...
         -m 25600 \
         -object '{"size": 26843545600, "mem-path": "/mnt/tmp", "id":
"mem-machine_mem", "qom-type": "memory-backend-file"}'  \
         -smp 60,maxcpus=3D60,cores=3D30,threads=3D1,clusters=3D1,sockets=
=3D2  \
       login guest:
       # nohup stress --vm 50 --vm-bytes 256M --timeout 30s >
/dev/null & ------> hit Call trace

On guest kernel:
2023-09-18 07:54:03: [   76.592706] CPU: 23 PID: 254 Comm:
kworker/23:1 Kdump: loaded Not tainted 6.6.0-rc2-zhenyzha_4k+ #3
2023-09-18 07:54:03: [   76.593782] Hardware name: QEMU KVM Virtual
Machine, BIOS edk2-20230524-3.el9 05/24/2023
2023-09-18 07:54:03: [   76.594641] Workqueue: rcu_gp wait_rcu_exp_gp
2023-09-18 07:54:03: [   76.595248] pstate: 80400005 (Nzcv daif +PAN
-UAO -TCO -DIT -SSBS BTYPE=3D--)
2023-09-18 07:54:03: [   76.596025] pc : smp_call_function_single+0xe4/0x1e=
8
2023-09-18 07:54:03: [   76.596833] lr :
__sync_rcu_exp_select_node_cpus+0x27c/0x428
2023-09-18 07:54:03: [   76.597534] sp : ffff800084a0bc60
2023-09-18 07:54:03: [   76.598078] x29: ffff800084a0bc60 x28:
ffff0003fdad9440 x27: 0000000000000001
2023-09-18 07:54:03: [   76.598874] x26: ffff800081a541b0 x25:
ffff800081e0af40 x24: ffff0000c425ed80
2023-09-18 07:54:03: [   76.599817] x23: 0000000000000004 x22:
ffff800081532fa0 x21: 0000000000000ffe
2023-09-18 07:54:03: [   76.600621] x20: ffff800081537440 x19:
ffff800084a0bca0 x18: 0000000000000001
2023-09-18 07:54:03: [   76.601420] x17: 0000000000000000 x16:
ffff800080f352e8 x15: 0000ffff97d02fff
2023-09-18 07:54:03: [   76.602212] x14: 0000000000000000 x13:
0000000000000030 x12: 0101010101010101
2023-09-18 07:54:03: [   76.603158] x11: ffff800081532fa0 x10:
0000000000000001 x9 : ffff80008014c714
2023-09-18 07:54:03: [   76.603963] x8 : ffff800081e03130 x7 :
ffff800081521008 x6 : ffff80008014e070
2023-09-18 07:54:03: [   76.604759] x5 : 0000000000000000 x4 :
ffff0003fda34c88 x3 : 0000000000000001
2023-09-18 07:54:03: [   76.605703] x2 : 0000000000000000 x1 :
ffff0003fda34c80 x0 : 000000000000001c
2023-09-18 07:54:03: [   76.606507] Call trace:
2023-09-18 07:54:03: [   76.606990]  smp_call_function_single+0xe4/0x1e8
2023-09-18 07:54:03: [   76.607617]  __sync_rcu_exp_select_node_cpus+0x27c/=
0x428
2023-09-18 07:54:03: [   76.608290]  sync_rcu_exp_select_cpus+0x164/0x2e0
2023-09-18 07:54:03: [   76.608963]  wait_rcu_exp_gp+0x1c/0x38
2023-09-18 07:54:03: [   76.609563]  process_one_work+0x174/0x3c8
2023-09-18 07:54:03: [   76.610181]  worker_thread+0x2c8/0x3e0
2023-09-18 07:54:03: [   76.610776]  kthread+0x100/0x110
2023-09-18 07:54:03: [   76.611330]  ret_from_fork+0x10/0x20
2023-09-18 07:54:15: [   88.396191] rcu: INFO: rcu_preempt detected
stalls on CPUs/tasks:
2023-09-18 07:54:15: [   88.397195] rcu: 11-...0: (18 ticks this GP)
idle=3D79ec/1/0x4000000000000000 softirq=3D577/579 fqs=3D1215
2023-09-18 07:54:15: [   88.398244] rcu: 25-...0: (1 GPs behind)
idle=3D599c/1/0x4000000000000000 softirq=3D300/301 fqs=3D1215
2023-09-18 07:54:15: [   88.399254] rcu: 33-...0: (36 ticks this GP)
idle=3De454/1/0x4000000000000000 softirq=3D717/719 fqs=3D1216
2023-09-18 07:54:15: [   88.400275] rcu: (detected by 19, t=3D6006
jiffies, g=3D1173, q=3D61327 ncpus=3D38)
2023-09-18 07:54:15: [   88.401135] Task dump for CPU 11:
2023-09-18 07:54:15: [   88.401711] task:stress          state:R
running task     stack:0     pid:3182  ppid:3178   flags:0x00000202
2023-09-18 07:54:15: [   88.402794] Call trace:
2023-09-18 07:54:15: [   88.403312]  __switch_to+0xc8/0x110
2023-09-18 07:54:15: [   88.403915]  do_page_fault+0x198/0x4e0
2023-09-18 07:54:15: [   88.404533]  do_translation_fault+0x38/0x68
2023-09-18 07:54:15: [   88.405169]  do_mem_abort+0x48/0xa0
2023-09-18 07:54:15: [   88.405771]  el0_da+0x4c/0x180
2023-09-18 07:54:15: [   88.406337]  el0t_64_sync_handler+0xdc/0x150
2023-09-18 07:54:15: [   88.406991]  el0t_64_sync+0x17c/0x180
2023-09-18 07:54:15: [   88.407601] Task dump for CPU 25:
2023-09-18 07:54:15: [   88.408182] task:stress          state:R
running task     stack:0     pid:3200  ppid:3178   flags:0x00000203
2023-09-18 07:54:15: [   88.409258] Call trace:
2023-09-18 07:54:15: [   88.409769]  __switch_to+0xc8/0x110
2023-09-18 07:54:15: [   88.410339]  0x440dc0
2023-09-18 07:54:15: [   88.410816] Task dump for CPU 33:
2023-09-18 07:54:15: [   88.411362] task:stress          state:R
running task     stack:0     pid:3191  ppid:3178   flags:0x00000203
2023-09-18 07:54:15: [   88.412403] Call trace:
2023-09-18 07:54:15: [   88.412866]  __switch_to+0xc8/0x110
2023-09-18 07:54:15: [   88.413405]  __memcg_kmem_charge_page+0x270/0x2c0
2023-09-18 07:54:15: [   88.414033]  __alloc_pages+0x100/0x278
2023-09-18 07:54:15: [   88.414585]  memcg_stock+0x0/0x58

On host kernel:
173242 Sep 18 08:57:51 virt-mtsnow-02 kernel: ------------[ cut here
]------------
173243 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
52 kernel messages
173244 Sep 18 08:57:51 virt-mtsnow-02 kernel: do_cow_fault+0xf0/0x300
173245 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
162 kernel messages
173246 Sep 18 08:57:51 virt-mtsnow-02 kernel: CPU: 14 PID: 11294 Comm:
qemu-kvm Tainted: G        W          6.6.0-rc2-zhenyzha-64k+ #1
173247 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
226 kernel messages
173248 Sep 18 08:57:51 virt-mtsnow-02 kernel: x21: 0000000000000000
173249 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
120 kernel messages
173250 Sep 18 08:57:51 virt-mtsnow-02 kernel: __do_fault+0x40/0x210
173251 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
39 kernel messages
173252 Sep 18 08:57:51 virt-mtsnow-02 kernel: do_el0_svc+0xb4/0xd0
173253 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
325 kernel messages
173254 Sep 18 08:57:51 virt-mtsnow-02 kernel: get_user_pages_unlocked+0xc4/=
0x3b8
173255 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
255 kernel messages
173256 Sep 18 08:57:51 virt-mtsnow-02 kernel: pci_hyperv_intf
i2c_designware_core
173257 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
87 kernel messages
173258 Sep 18 08:57:51 virt-mtsnow-02 kernel: xfs_filemap_fault+0x54/0x68 [=
xfs]
173259 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
248 kernel messages
173260 Sep 18 08:57:51 virt-mtsnow-02 kernel: pci_hyperv_intf
173261 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
69 kernel messages
173262 Sep 18 08:57:51 virt-mtsnow-02 kernel: Hardware name: GIGABYTE
R152-P31-00/MP32-AR1-00, BIOS F18v (SCP: 1.08.20211002) 12/01/2021
173263 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
297 kernel messages
173264 Sep 18 08:57:51 virt-mtsnow-02 kernel: __filemap_add_folio+0x33c/0x4=
e0
173265 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
12 kernel messages
173266 Sep 18 08:57:51 virt-mtsnow-02 kernel: x26: 0000000000000001
173267 Sep 18 08:57:51 virt-mtsnow-02 systemd-journald[15184]: Missed
74 kernel messages

[ 5456.588346] ------------[ cut here ]------------
[ 5456.588358]  x10: 000000000000000a
[ 5456.588365]  dm_mod
[ 5456.588372]  nft_compat
[ 5456.588374] Hardware name: GIGABYTE R152-P31-00/MP32-AR1-00, BIOS
F18v (SCP: 1.08.20211002) 12/01/2021
[ 5456.588417]  fat
[ 5456.588421]  x16: 000000009872d4d0
[ 5456.588430]  ipmi_msghandler arm_cmn
[ 5456.588439]  x10: 000000000000000a
[ 5456.588414]  __xfs_filemap_fault+0x60/0x3c0 [xfs]
[ 5456.588454] x5 : 0000000000000028
[ 5456.588460]  nvme_core
[ 5456.588474]  pci_hyperv_intf
[ 5456.588482] ------------[ cut here ]------------
[ 5456.588488]  page_cache_async_ra+0x64/0xa8
[ 5456.588491]  filemap_fault+0x238/0xaa8
[ 5456.588506]  nf_defrag_ipv4 nf_tables
[ 5456.588514]  nfs_acl
[ 5456.588518]  x22: ffffffc202880000
[ 5456.588525]  netfs
[ 5456.588527]  stp

[ 5456.588539]  acpi_ipmi
[ 5456.588546]  x10: 000000000000000a
[ 5456.588554]  x7 : ffff07ffa0a67210
[ 5456.588562]  get_user_pages_unlocked+0xc4/0x3b8
[ 5456.588567]  __gfn_to_pfn_memslot+0xa4/0xf8
[ 5456.588575]  xas_split_alloc+0xf8/0x128
[ 5456.588581]  sha1_ce
[ 5456.588588]  i2c_algo_bit
[ 5456.588592]  page_cache_async_ra+0x64/0xa8


Using @gshan@redhat.com 's patch:KVM: arm64: Fix soft-lockup on
relaxing PTE permission
Still hit Call trace:
2023-09-18 10:56:20: [   57.494201] watchdog: BUG: soft lockup -
CPU#58 stuck for 22s! [gsd-power:4858]
2023-09-18 10:56:20: [   57.495674] Modules linked in: nft_fib_inet
nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4
nf_reject_ipv6 nft_reject nft_ct nft_chain_nat nf_nat nf_conntrack
nf_defrag_ipv6 nf_defrag_ipv4 rfkill ip_set nf_tables nfnetlink qrtr
vfat fat fuse xfs libcrc32c virtio_gpu virtio_dma_buf drm_shmem_helper
nvme_tcp drm_kms_helper nvme_fabrics nvme_core nvme_common sg drm
crct10dif_ce ghash_ce sha2_ce sha256_arm64 sha1_ce virtio_net
net_failover virtio_scsi failover virtio_mmio dm_multipath dm_mirror
dm_region_hash dm_log dm_mod be2iscsi cxgb4i cxgb4 tls libcxgbi
libcxgb qla4xxx iscsi_boot_sysfs iscsi_tcp libiscsi_tcp libiscsi
scsi_transport_iscsi
2023-09-18 10:56:20: [   57.501871] CPU: 58 PID: 4858 Comm: gsd-power
Kdump: loaded Not tainted 6.6.0-rc2-zhenyzha_4k+ #3
2023-09-18 10:56:20: [   57.502719] Hardware name: QEMU KVM Virtual
Machine, BIOS edk2-20230524-3.el9 05/24/2023
2023-09-18 10:56:20: [   57.503540] pstate: 20400005 (nzCv daif +PAN
-UAO -TCO -DIT -SSBS BTYPE=3D--)
2023-09-18 10:56:20: [   57.504612] pc : smp_call_function_many_cond+0x16c/=
0x618
2023-09-18 10:56:20: [   57.505425] lr : smp_call_function_many_cond+0x188/=
0x618
2023-09-18 10:56:20: [   57.505974] sp : ffff8000870f38f0
2023-09-18 10:56:20: [   57.506370] x29: ffff8000870f38f0 x28:
000000000000003c x27: ffff00063c5dcaa0
2023-09-18 10:56:20: [   57.507041] x26: 000000000000003c x25:
000000000000003b x24: ffff00063c5b6848
2023-09-18 10:56:20: [   57.507812] x23: 0000000000000000 x22:
ffff00063c5b6848 x21: ffff800081a541b0
2023-09-18 10:56:20: [   57.508513] x20: ffff00063c5b6840 x19:
ffff800081a4f840 x18: 0000000000000014
2023-09-18 10:56:20: [   57.509247] x17: 00000000fd875552 x16:
0000000044ca0210 x15: 000000005df1120b
2023-09-18 10:56:20: [   57.509947] x14: 00000000ac15cb21 x13:
00000000b7ff1817 x12: 0000000006d3918c
2023-09-18 10:56:20: [   57.510645] x11: 00000000ba65fdab x10:
00000000f60c2b88 x9 : ffff80008061a9dc
2023-09-18 10:56:20: [   57.511264] x8 : ffff00063c5b6a50 x7 :
0000000000000000 x6 : 0000000001000000
2023-09-18 10:56:20: [   57.511817] x5 : 000000000000003c x4 :
0000000000000007 x3 : ffff00063bf28aa8
2023-09-18 10:56:20: [   57.512415] x2 : 0000000000000000 x1 :
0000000000000011 x0 : 0000000000000007
2023-09-18 10:56:20: [   57.513092] Call trace:
2023-09-18 10:56:20: [   57.515105]  smp_call_function_many_cond+0x16c/0x61=
8
2023-09-18 10:56:20: [   57.515684]  kick_all_cpus_sync+0x48/0x80
2023-09-18 10:56:20: [   57.516039]  flush_icache_range+0x40/0x60
2023-09-18 10:56:20: [   57.516413]  bpf_int_jit_compile+0x1ac/0x5f8
2023-09-18 10:56:20: [   57.516821]  bpf_prog_select_runtime+0xd4/0x110
2023-09-18 10:56:20: [   57.517279]  bpf_prepare_filter+0x1e8/0x220
2023-09-18 10:56:20: [   57.517727]  __get_filter+0xdc/0x180
2023-09-18 10:56:20: [   57.518231]  sk_attach_filter+0x1c/0xb0
2023-09-18 10:56:20: [   57.518605]  sk_setsockopt+0x9dc/0x1230
2023-09-18 10:56:20: [   57.518909]  sock_setsockopt+0x18/0x28
2023-09-18 10:56:20: [   57.519177]  __sys_setsockopt+0x164/0x190
2023-09-18 10:56:20: [   57.519501]  __arm64_sys_setsockopt+0x2c/0x40
2023-09-18 10:56:20: [   57.519911]  invoke_syscall.constprop.0+0x7c/0xd0
2023-09-18 10:56:20: [   57.520345]  do_el0_svc+0xb4/0xd0
2023-09-18 10:56:20: [   57.520670]  el0_svc+0x50/0x228
2023-09-18 10:56:20: [   57.521331]  el0t_64_sync_handler+0x134/0x150
2023-09-18 10:56:20: [   57.521758]  el0t_64_sync+0x17c/0x180
2023-09-18 10:56:23: [   60.724199] watchdog: BUG: soft lockup -
CPU#28 stuck for 26s! [(fwupd):5108]

[ 6253.928601] CPU: 64 PID: 18885 Comm: qemu-kvm Kdump: loaded
Tainted: G        W          6.6.0-rc1-zhenyzha_64k+ #2
[ 6253.939021] Hardware name: GIGABYTE R152-P31-00/MP32-AR1-00, BIOS
F31n (SCP: 2.10.20220810) 09/30/2022
[ 6253.948312] pstate: 80400009 (Nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=
=3D--)
[ 6253.955262] pc : xas_split_alloc+0xf8/0x128
[ 6253.959432] lr : __filemap_add_folio+0x33c/0x4e0
[ 6253.964037] sp : ffff80008b10f210
[ 6253.967338] x29: ffff80008b10f210 x28: ffffba8c43708c00 x27: 00000000000=
00001
[ 6253.974461] x26: 0000000000000001 x25: ffffffffffffc005 x24: 00000000000=
00000
[ 6253.981583] x23: ffff80008b10f2c0 x22: 00000a36da000101 x21: 00000000000=
00000
[ 6253.988706] x20: ffffffc203be2a00 x19: 000000000000000d x18: 00000000000=
00014
[ 6253.995828] x17: 00000000be237f61 x16: 000000001baa68cc x15: ffffba8c429=
a5944
[ 6254.002950] x14: ffffba8c429b57bc x13: ffffba8c429a5944 x12: ffffba8c429=
b57bc
[ 6254.010073] x11: ffffba8c4297160c x10: ffffba8c4365d414 x9 : ffffba8c436=
5857c
[ 6254.017195] x8 : ffff80008b10f210 x7 : ffff07ffa1304900 x6 : ffff80008b1=
0f210
[ 6254.024317] x5 : 000000000000000e x4 : 0000000000000000 x3 : 00000000000=
12c40
[ 6254.031439] x2 : 000000000000000d x1 : 000000000000000c x0 : 00000000000=
00000
[ 6254.038562] Call trace:
[ 6254.040995]  xas_split_alloc+0xf8/0x128
[ 6254.044818]  __filemap_add_folio+0x33c/0x4e0
[ 6254.049076]  filemap_add_folio+0x48/0xd0
[ 6254.052986]  page_cache_ra_unbounded+0xf0/0x1f0
[ 6254.057504]  page_cache_ra_order+0x8c/0x310
[ 6254.061675]  filemap_fault+0x67c/0xaa8
[ 6254.065412]  __xfs_filemap_fault+0x60/0x3c0 [xfs]
[ 6254.070163]  xfs_filemap_fault+0x54/0x68 [xfs]
[ 6254.074651]  __do_fault+0x40/0x210
[ 6254.078040]  do_cow_fault+0xf0/0x300
[ 6254.081602]  do_pte_missing+0x140/0x238
[ 6254.085426]  handle_pte_fault+0x100/0x160
[ 6254.089423]  __handle_mm_fault+0x100/0x310
[ 6254.093506]  handle_mm_fault+0x6c/0x270
[ 6254.097330]  faultin_page+0x70/0x128
[ 6254.100893]  __get_user_pages+0xc8/0x2d8
[ 6254.104802]  get_user_pages_unlocked+0xc4/0x3b8
[ 6254.109320]  hva_to_pfn+0xf8/0x468
[ 6254.112709]  __gfn_to_pfn_memslot+0xa4/0xf8
[ 6254.116879]  user_mem_abort+0x174/0x7e8
[ 6254.120702]  kvm_handle_guest_abort+0x2dc/0x450
[ 6254.125220]  handle_exit+0x70/0x1c8
[ 6254.128696]  kvm_arch_vcpu_ioctl_run+0x224/0x5b8
[ 6254.133300]  kvm_vcpu_ioctl+0x28c/0x9d0
[ 6254.137123]  __arm64_sys_ioctl+0xa8/0xf0
[ 6254.141033]  invoke_syscall.constprop.0+0x7c/0xd0
[ 6254.145725]  do_el0_svc+0xb4/0xd0
[ 6254.149028]  el0_svc+0x50/0x228
[ 6254.152157]  el0t_64_sync_handler+0x134/0x150
[ 6254.156501]  el0t_64_sync+0x17c/0x180
[ 6254.160151] ---[ end trace 0000000000000000 ]---
[ 6254.164766] ------------[ cut here ]------------
[ 6254.169370] WARNING: CPU: 64 PID: 18885 at lib/xarray.c:1010
xas_split_alloc+0xf8/0x128
[ 6254.177361] Modules linked in: loop isofs cdrom vhost_net vhost
vhost_iotlb tap tun bluetooth tls nfsv3 rpcsec_gss_krb5 nfsv4
dns_resolver nfs fscache netfs rpcrdma rdma_cm iw_cm ib_cm ib_core
xt_CHECKSUM xt_MASQUERADE xt_conntrack ipt_REJECT nf_reject_ipv4
nft_compat nft_chain_nat nf_nat nf_conntrack nf_defrag_ipv6
nf_defrag_ipv4 nf_tables nfnetlink bridge stp llc rfkill vfat fat ast
drm_shmem_helper drm_kms_helper acpi_ipmi ipmi_ssif arm_spe_pmu
ipmi_devintf ipmi_msghandler arm_cmn arm_dmc620_pmu arm_dsu_pmu
cppc_cpufreq drm fuse nfsd auth_rpcgss nfs_acl lockd grace sunrpc xfs
libcrc32c crct10dif_ce ghash_ce igb sha2_ce sha256_arm64 sha1_ce
sbsa_gwdt i2c_designware_platform i2c_algo_bit i2c_designware_core
xgene_hwmon sg dm_mirror dm_region_hash dm_log dm_mod


Tested-by: Zhenyu Zhang <zhenyzha@redhat.com>

On Mon, Sep 4, 2023 at 1:20=E2=80=AFAM Joel Fernandes (Google)
<joel@joelfernandes.org> wrote:
>
> Hello!
>
> Here is v6 of the mremap start address optimization / fix for exec warnin=
g.
> Should be hopefully final now and only 2/7 and 6/7 need a tag. Thanks a l=
ot to
> Lorenzo and Linus for the detailed reviews.
>
> Description of patches
> =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D
> These patches optimizes the start addresses in move_page_tables() and tes=
ts the
> changes. It addresses a warning [1] that occurs due to a downward, overla=
pping
> move on a mutually-aligned offset within a PMD during exec. By initiating=
 the
> copy process at the PMD level when such alignment is present, we can prev=
ent
> this warning and speed up the copying process at the same time. Linus Tor=
valds
> suggested this idea. Check the individual patches for more details.
> [1] https://lore.kernel.org/all/ZB2GTBD%2FLWTrkOiO@dhcp22.suse.cz/
>
> History of patches:
> v5->v6:
> 1. Reworking the stack case a bit more and tested it (should be final now=
).
> 2. Other small nits.
>
> v4->v5:
> 1. Rebased on mainline.
> 2. Several improvement suggestions from Lorenzo.
>
> v3->v4:
> 1. Care to be taken to move purely within a VMA, in other words this chec=
k
>    in call_align_down():
>     if (vma->vm_start !=3D addr_masked)
>             return false;
>
>     As an example of why this is needed:
>     Consider the following range which is 2MB aligned and is
>     a part of a larger 10MB range which is not shown. Each
>     character is 256KB below making the source and destination
>     2MB each. The lower case letters are moved (s to d) and the
>     upper case letters are not moved.
>
>     |DDDDddddSSSSssss|
>
>     If we align down 'ssss' to start from the 'SSSS', we will end up dest=
roying
>     SSSS. The above if statement prevents that and I verified it.
>
>     I also added a test for this in the last patch.
>
> 2. Handle the stack case separately. We do not care about #1 for stack mo=
vement
>    because the 'SSSS' does not matter during this move. Further we need t=
o do this
>    to prevent the stack move warning.
>
>     if (!for_stack && vma->vm_start <=3D addr_masked)
>             return false;
>
> v2->v3:
> 1. Masked address was stored in int, fixed it to unsigned long to avoid t=
runcation.
> 2. We now handle moves happening purely within a VMA, a new test is added=
 to handle this.
> 3. More code comments.
>
> v1->v2:
> 1. Trigger the optimization for mremaps smaller than a PMD. I tested by t=
racing
> that it works correctly.
>
> 2. Fix issue with bogus return value found by Linus if we broke out of th=
e
> above loop for the first PMD itself.
>
> v1: Initial RFC.
>
> Joel Fernandes (1):
> selftests: mm: Add a test for moving from an offset from start of
> mapping
>
> Joel Fernandes (Google) (6):
> mm/mremap: Optimize the start addresses in move_page_tables()
> mm/mremap: Allow moves within the same VMA for stack moves
> selftests: mm: Fix failure case when new remap region was not found
> selftests: mm: Add a test for mutually aligned moves > PMD size
> selftests: mm: Add a test for remapping to area immediately after
> existing mapping
> selftests: mm: Add a test for remapping within a range
>
> fs/exec.c                                |   2 +-
> include/linux/mm.h                       |   2 +-
> mm/mremap.c                              |  73 +++++-
> tools/testing/selftests/mm/mremap_test.c | 301 +++++++++++++++++++----
> 4 files changed, 329 insertions(+), 49 deletions(-)
>
> --
> 2.42.0.283.g2d96d420d3-goog
>