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

Signed-off-by: jia.he@hxt-semitech.com
---
v2: refine the codes as suggested by Claudio Imbrenda

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

diff --git a/mm/ksm.c b/mm/ksm.c
index e3cbf9a..e6a9640 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 +2572,15 @@ 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)
+
+ /* 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
@@ -2587,8 +2594,7 @@ 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 (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
anon_vma_unlock_read(anon_vma);
return;
}
--
1.8.3.1
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