Re: [PATCH v2] mm/ksm: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm

From: Andrew Morton
Date: Thu Jun 07 2018 - 18:13:51 EST

On Thu, 24 May 2018 13:38:05 -0700 Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> wrote:
> >
> > Jia, Andrew,
> >
> > What is the status of this patch ?
> >
>
> I have it scheduled for 4.18-rc1, with a cc:stable for backporting.
>
> I'd normally put such a fix into 4.17-rcX but I'd like to give Hugh
> time to review it and to generally give it a bit more time for review
> and test.
>
> Have you tested it yourself?

I'll take your silence as a no.

This patch is quite urgent and is tagged for -stable backporting, yet
it remains in an unreviewed state. Any takers?



From: Jia He <jia.he@xxxxxxxxxxxxxxxx>
Subject: mm/ksm.c: ignore STABLE_FLAG of rmap_item->address in rmap_walk_ksm()

In our armv8a server(QDF2400), I noticed lots of WARN_ON caused by
PAGE_SIZE unaligned for rmap_item->address under memory pressure
tests(start 20 guests and run memhog in the host).

--------------------------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 will cause exceptions in handle_hva_to_gpa on arm64.

This patch fixes it by ignoring (not removing) the low bits of address
when doing rmap_walk_ksm.

IMO, it should be backported to stable tree. the stom of WARN_ONs is
very easy for me to reproduce. More than that, I watched a panic (not
reproducible) as follows:

[35380.805825] page:ffff7fe003742d80 count:-4871 mapcount:-2126053375
mapping: (null) index:0x0
[35380.815024] flags: 0x1fffc00000000000()
[35380.818845] raw: 1fffc00000000000 0000000000000000 0000000000000000
ffffecf981470000
[35380.826569] raw: dead000000000100 dead000000000200 ffff8017c001c000
0000000000000000
[35380.834294] page dumped because: nonzero _refcount
[35380.839069] Modules linked in: vhost_net vhost tap ebtable_filter ebtables
ip6table_filter ip6_tables iptable_filter fcoe libfcoe libfc 8021q garp mrp stp
llc scsi_transport_fc openvswitch nf_conntrack_ipv6 nf_nat_ipv6
nf_conntrack_ipv4 nf_defrag_ipv4 nf_nat_ipv4 nf_defrag_ipv6 nf_nat nf_conntrack
vfat fat 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_uverbs ib_umad rdma_cm ib_cm iw_cm mlx5_ib ib_core crc32_ce ipmi_ssif tpm_tis
tpm_tis_core sg nfsd auth_rpcgss nfs_acl lockd grace sunrpc dm_multipath
ip_tables xfs libcrc32c mlx5_core mlxfw devlink ahci_platform libahci_platform
libahci qcom_emac sdhci_acpi sdhci hdma mmc_core hdma_mgmt i2c_qup dm_mirror
dm_region_hash dm_log dm_mod
[35380.908341] CPU: 29 PID: 18323 Comm: qemu-kvm Tainted: G W
4.14.15-5.hxt.aarch64 #1
[35380.917107] Hardware name: <snip for confidential issues>
[35380.930909] Call trace:
[35380.933345] [<ffff000008088f00>] dump_backtrace+0x0/0x22c
[35380.938723] [<ffff000008089150>] show_stack+0x24/0x2c
[35380.943759] [<ffff00000893c078>] dump_stack+0x8c/0xb0
[35380.948794] [<ffff00000820ab50>] bad_page+0xf4/0x154
[35380.953740] [<ffff000008211ce8>] free_pages_check_bad+0x90/0x9c
[35380.959642] [<ffff00000820c430>] free_pcppages_bulk+0x464/0x518
[35380.965545] [<ffff00000820db98>] free_hot_cold_page+0x22c/0x300
[35380.971448] [<ffff0000082176fc>] __put_page+0x54/0x60
[35380.976484] [<ffff0000080b1164>] unmap_stage2_range+0x170/0x2b4
[35380.982385] [<ffff0000080b12d8>] kvm_unmap_hva_handler+0x30/0x40
[35380.988375] [<ffff0000080b0104>] handle_hva_to_gpa+0xb0/0xec
[35380.994016] [<ffff0000080b2644>] kvm_unmap_hva_range+0x5c/0xd0
[35380.999833] [<ffff0000080a8054>]

I even injected a fault on purpose in kvm_unmap_hva_range by seting
size=size-0x200, the call trace is similar as above. So I thought the
panic is similarly caused by the root cause of WARN_ON.

Link: http://lkml.kernel.org/r/1525403506-6750-1-git-send-email-hejianet@xxxxxxxxx
Signed-off-by: Jia He <jia.he@xxxxxxxxxxxxxxxx>
Cc: Suzuki K Poulose <Suzuki.Poulose@xxxxxxx>
Cc: Andrea Arcangeli <aarcange@xxxxxxxxxx>
Cc: Minchan Kim <minchan@xxxxxxxxxx>
Cc: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxxxxxxx>
Cc: Arvind Yadav <arvind.yadav.cs@xxxxxxxxx>
Cc: Mike Rapoport <rppt@xxxxxxxxxxxxxxxxxx>
Cc: Jia He <hejianet@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

mm/ksm.c | 14 ++++++++++----
1 file changed, 10 insertions(+), 4 deletions(-)

diff -puN mm/ksm.c~mm-ksm-ignore-stable_flag-of-rmap_item-address-in-rmap_walk_ksm mm/ksm.c
--- a/mm/ksm.c~mm-ksm-ignore-stable_flag-of-rmap_item-address-in-rmap_walk_ksm
+++ a/mm/ksm.c
@@ -216,6 +216,8 @@ 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 };
@@ -2598,10 +2600,15 @@ again:
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)
+
+ /* Ignore the stable/unstable/sqnr flags */
+ addr = rmap_item->address & ~KSM_FLAG_MASK;
+
+ if (addr < vma->vm_start || addr >= vma->vm_end)
continue;
/*
* Initially we examine only the vma which covers this
@@ -2615,8 +2622,7 @@ again:
if (rwc->invalid_vma && rwc->invalid_vma(vma, rwc->arg))
continue;

- if (!rwc->rmap_one(page, vma,
- rmap_item->address, rwc->arg)) {
+ if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
anon_vma_unlock_read(anon_vma);
return;
}
_