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

[Jia He <hejianet@gmail.com>]

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;
+			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;
+
+			if (!rwc->rmap_one(page, vma, addr, rwc->arg)) {
 				anon_vma_unlock_read(anon_vma);
 				return;
 			}
-- 
1.8.3.1