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SubjectRe: [PATCH] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm
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On 5/3/2018 6:44 PM, Claudio Imbrenda Wrote:
> On Thu, 3 May 2018 16:34:48 +0800
> Jia He <hejianet@gmail.com> wrote:
>
>> In our armv8a server(QDF2400), I noticed a WARN_ON caused by PAGE_SIZE
>> unaligned for rmap_item->address.
>>
>> --------------------------begin--------------------------------------
>> [ 410.853828] WARNING: CPU: 4 PID: 4641 at
>> arch/arm64/kvm/../../../virt/kvm/arm/mmu.c:1826
>> kvm_age_hva_handler+0xc0/0xc8
>> [ 410.864518] Modules linked in: vhost_net vhost tap xt_CHECKSUM
>> ipt_MASQUERADE nf_nat_masquerade_ipv4 ip6t_rpfilter ipt_REJECT
>> nf_reject_ipv4 ip6t_REJECT nf_reject_ipv6 xt_conntrack ip_set
>> nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_nat
>> nf_conntrack_ipv6 nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle
>> ip6table_security ip6table_raw iptable_nat nf_conntrack_ipv4
>> nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle
>> iptable_security iptable_raw ebtable_filter ebtables ip6table_filter
>> ip6_tables iptable_filter rpcrdma ib_isert iscsi_target_mod ib_iser
>> libiscsi scsi_transport_iscsi ib_srpt target_core_mod ib_srp
>> scsi_transport_srp ib_ipoib rdma_ucm ib_ucm ib_umad rdma_cm ib_cm
>> iw_cm mlx5_ib vfat fat ib_uverbs dm_mirror dm_region_hash ib_core
>> dm_log dm_mod crc32_ce ipmi_ssif sg nfsd [ 410.935101] auth_rpcgss
>> nfs_acl lockd grace sunrpc ip_tables xfs libcrc32c mlx5_core ixgbe
>> mlxfw devlink mdio ahci_platform libahci_platform qcom_emac libahci
>> hdma hdma_mgmt i2c_qup [ 410.951369] CPU: 4 PID: 4641 Comm: memhog
>> Tainted: G W 4.17.0-rc3+ #8
>> [ 410.959104] Hardware name: <snip for confidential issues>
>> [ 410.969791] pstate: 80400005 (Nzcv daif +PAN -UAO)
>> [ 410.974575] pc : kvm_age_hva_handler+0xc0/0xc8
>> [ 410.979012] lr : handle_hva_to_gpa+0xa8/0xe0
>> [ 410.983274] sp : ffff801761553290
>> [ 410.986581] x29: ffff801761553290 x28: 0000000000000000
>> [ 410.991888] x27: 0000000000000002 x26: 0000000000000000
>> [ 410.997195] x25: ffff801765430058 x24: ffff0000080b5608
>> [ 411.002501] x23: 0000000000000000 x22: ffff8017ccb84000
>> [ 411.007807] x21: 0000000003ff0000 x20: ffff8017ccb84000
>> [ 411.013113] x19: 000000000000fe00 x18: ffff000008fb3c08
>> [ 411.018419] x17: 0000000000000000 x16: 0060001645820bd3
>> [ 411.023725] x15: ffff80176aacbc08 x14: 0000000000000000
>> [ 411.029031] x13: 0000000000000040 x12: 0000000000000228
>> [ 411.034337] x11: 0000000000000000 x10: 0000000000000000
>> [ 411.039643] x9 : 0000000000000010 x8 : 0000000000000004
>> [ 411.044949] x7 : 0000000000000000 x6 : 00008017f0770000
>> [ 411.050255] x5 : 0000fffda59f0200 x4 : 0000000000000000
>> [ 411.055561] x3 : 0000000000000000 x2 : 000000000000fe00
>> [ 411.060867] x1 : 0000000003ff0000 x0 : 0000000020000000
>> [ 411.066173] Call trace:
>> [ 411.068614] kvm_age_hva_handler+0xc0/0xc8
>> [ 411.072703] handle_hva_to_gpa+0xa8/0xe0
>> [ 411.076619] kvm_age_hva+0x4c/0xe8
>> [ 411.080014] kvm_mmu_notifier_clear_flush_young+0x54/0x98
>> [ 411.085408] __mmu_notifier_clear_flush_young+0x6c/0xa0
>> [ 411.090627] page_referenced_one+0x154/0x1d8
>> [ 411.094890] rmap_walk_ksm+0x12c/0x1d0
>> [ 411.098632] rmap_walk+0x94/0xa0
>> [ 411.101854] page_referenced+0x194/0x1b0
>> [ 411.105770] shrink_page_list+0x674/0xc28
>> [ 411.109772] shrink_inactive_list+0x26c/0x5b8
>> [ 411.114122] shrink_node_memcg+0x35c/0x620
>> [ 411.118211] shrink_node+0x100/0x430
>> [ 411.121778] do_try_to_free_pages+0xe0/0x3a8
>> [ 411.126041] try_to_free_pages+0xe4/0x230
>> [ 411.130045] __alloc_pages_nodemask+0x564/0xdc0
>> [ 411.134569] alloc_pages_vma+0x90/0x228
>> [ 411.138398] do_anonymous_page+0xc8/0x4d0
>> [ 411.142400] __handle_mm_fault+0x4a0/0x508
>> [ 411.146489] handle_mm_fault+0xf8/0x1b0
>> [ 411.150321] do_page_fault+0x218/0x4b8
>> [ 411.154064] do_translation_fault+0x90/0xa0
>> [ 411.158239] do_mem_abort+0x68/0xf0
>> [ 411.161721] el0_da+0x24/0x28
>> ---------------------------end---------------------------------------
>>
>> In rmap_walk_ksm, the rmap_item->address might still have the
>> STABLE_FLAG, then the start and end in handle_hva_to_gpa might not be
>> PAGE_SIZE aligned. Thus it causes exceptions in handle_hva_to_gpa on
>> arm64.
>>
>> This patch fixes it by ignoring the low bits of rmap_item->address
>> when doing rmap_walk_ksm.
>>
>> Signed-off-by: jia.he@hxt-semitech.com
>> ---
>> mm/ksm.c | 15 +++++++++++----
>> 1 file changed, 11 insertions(+), 4 deletions(-)
>>
>> diff --git a/mm/ksm.c b/mm/ksm.c
>> index e3cbf9a..3f0d980 100644
>> --- a/mm/ksm.c
>> +++ b/mm/ksm.c
>> @@ -199,6 +199,8 @@ struct rmap_item {
>> #define SEQNR_MASK 0x0ff /* low bits of unstable tree
>> seqnr */ #define UNSTABLE_FLAG 0x100 /* is a node of
>> the unstable tree */ #define STABLE_FLAG 0x200 /* is
>> listed from the stable tree */ +#define KSM_FLAG_MASK
>> (SEQNR_MASK|UNSTABLE_FLAG|STABLE_FLAG)
>> + /* to mask all the flags */
>>
>> /* The stable and unstable tree heads */
>> static struct rb_root one_stable_tree[1] = { RB_ROOT };
>> @@ -2570,10 +2572,13 @@ void rmap_walk_ksm(struct page *page, struct
>> rmap_walk_control *rwc) anon_vma_lock_read(anon_vma);
>> anon_vma_interval_tree_foreach(vmac,
>> &anon_vma->rb_root, 0, ULONG_MAX) {
>> + unsigned long addr;
>> +
>> cond_resched();
>> vma = vmac->vma;
>> - if (rmap_item->address < vma->vm_start ||
>> - rmap_item->address >= vma->vm_end)
>> +
>> + addr = rmap_item->address;
> why not just: addr = rmap_item->address & ~KSM_FLAG_MASK;
yes, thank you.

Cheers,
Jia
>> + if (addr < vma->vm_start || addr >=
>> vma->vm_end) continue;
>> /*
>> * Initially we examine only the vma which
>> covers this @@ -2587,8 +2592,10 @@ void rmap_walk_ksm(struct page
>> *page, struct rmap_walk_control *rwc) if (rwc->invalid_vma &&
>> rwc->invalid_vma(vma, rwc->arg)) continue;
>>
>> - if (!rwc->rmap_one(page, vma,
>> - rmap_item->address,
>> rwc->arg)) {
>> + if (addr & STABLE_FLAG)
>> + addr &= ~KSM_FLAG_MASK;
> then you would not need the IF above, and it would be more readable.
>
>> +
>> + if (!rwc->rmap_one(page, vma, addr,
>> rwc->arg)) { anon_vma_unlock_read(anon_vma);
>> return;
>> }
>
> best regards,
>
> Claudio Imbrenda
>
>

--
Cheers,
Jia

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