linux-kernel - Re: [PATCH] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk

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Date:   Thu, 3 May 2018 21:23:03 +0800
From:   Jia He <hejianet@...il.com>
To:     Claudio Imbrenda <imbrenda@...ux.vnet.ibm.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Minchan Kim <minchan@...nel.org>,
        Arvind Yadav <arvind.yadav.cs@...il.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, jia.he@...-semitech.com
Subject: Re: [PATCH] mm/ksm: ignore STABLE_FLAG of rmap_item->address in
 rmap_walk_ksm



On 5/3/2018 6:44 PM, Claudio Imbrenda Wrote:
> On Thu,  3 May 2018 16:34:48 +0800
> Jia He <hejianet@...il.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@...-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