Re: [PATCH] KVM: arm/arm64: fix unaligned hva start and end in handle_hva_to_gpa

From: Jia He
Date: Wed May 02 2018 - 23:20:13 EST



On 5/3/2018 10:02 AM, Jia He Wrote:
Hi Marc

Thanks for the review


On 5/2/2018 10:26 PM, Marc Zyngier Wrote:
[+ Suzuki]

On 02/05/18 08:08, Jia He wrote:
From: Jia He <jia.he@xxxxxxxxxxxxxxxx>

In our armv8a server (QDF2400), I noticed a WARN_ON as follows:

[ 800.202850] WARNING: CPU: 33 PID: 255 at arch/arm64/kvm/../../../virt/kvm/arm/mmu.c:1670 kvm_age_hva_handler+0xcc/0xd4
Which kernel version is that? I don't have a WARN_ON() at this line in
4.17. Do you have a reproducer?
My running kernel version is v4.14-15, but I can reproduced it in 4.17 (start 20
guests and run memhog in the host)
In 4.17, the warn_on is at
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/virt/kvm/arm/mmu.c#n1826
[ 800.213535] 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_uverbs ib_umad rdma_cm ib_cm vfat fat iw_cm mlx5_ib ib_core dm_mirror dm_region_hash dm_log dm_mod crc32_ce ipmi_ssif sg nfsd
[ 800.284115] 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
[ 800.300382] CPU: 33 PID: 255 Comm: khugepaged Tainted: G W 4.14.36+ #6
[ 800.308030] Hardware name: <snip for confidential issues>
Well, that's QDF2400, right? ;-)
yes, exactly :)
[ 800.318717] task: ffff8017c949c000 task.stack: ffff8017c9498000
[ 800.324629] PC is at kvm_age_hva_handler+0xcc/0xd4
[ 800.329412] LR is at handle_hva_to_gpa+0xec/0x15c
[ 800.334109] pc : [<ffff0000080b4f2c>] lr : [<ffff0000080b4838>] pstate: 20400145
[ 800.341496] sp : ffff8017c949b260
[ 800.344804] x29: ffff8017c949b260 x28: ffff801663e25008
[ 800.350110] x27: 0000000000020000 x26: 00000001fb1a0000
[ 800.355416] x25: 0000ffff605b0200 x24: 0000ffff605a0200
[ 800.360722] x23: 0000000000000000 x22: 000000000000ffff
[ 800.366028] x21: 00000001fb1a0000 x20: ffff8017c085a000
[ 800.371334] x19: ffff801663e20008 x18: 0000000000000000
[ 800.376641] x17: 0000000000000000 x16: 0000000000000000
[ 800.381947] x15: 0000000000000000 x14: 3d646e655f617668
[ 800.387254] x13: 2c30303230623530 x12: 36666666663d646e
[ 800.392560] x11: 652c303032306135 x10: 3036666666663d74
[ 800.397867] x9 : 0000000000003796 x8 : 655f6e66672c3030
[ 800.403173] x7 : ffff00000859434c x6 : ffff8017f9c30cb8
[ 800.408479] x5 : ffff8017f9c30cb8 x4 : ffff0000080b4e60
[ 800.413786] x3 : 0000000000000000 x2 : 0000000000020000
[ 800.419092] x1 : 00000001fb1a0000 x0 : 0000000020000000
[ 800.424398] Call trace:
[ 800.426838] Exception stack(0xffff8017c949b120 to 0xffff8017c949b260)
[ 800.433272] b120: 0000000020000000 00000001fb1a0000 0000000000020000 0000000000000000
[ 800.441095] b140: ffff0000080b4e60 ffff8017f9c30cb8 ffff8017f9c30cb8 ffff00000859434c
[ 800.448918] b160: 655f6e66672c3030 0000000000003796 3036666666663d74 652c303032306135
[ 800.456740] b180: 36666666663d646e 2c30303230623530 3d646e655f617668 0000000000000000
[ 800.464563] b1a0: 0000000000000000 0000000000000000 0000000000000000 ffff801663e20008
[ 800.472385] b1c0: ffff8017c085a000 00000001fb1a0000 000000000000ffff 0000000000000000
[ 800.480208] b1e0: 0000ffff605a0200 0000ffff605b0200 00000001fb1a0000 0000000000020000
[ 800.488030] b200: ffff801663e25008 ffff8017c949b260 ffff0000080b4838 ffff8017c949b260
[ 800.495853] b220: ffff0000080b4f2c 0000000020400145 0000000000000001 ffff8017c949b2a0
[ 800.503676] b240: ffffffffffffffff ffff8017c949b260 ffff8017c949b260 ffff0000080b4f2c
[ 800.511498] [<ffff0000080b4f2c>] kvm_age_hva_handler+0xcc/0xd4
[ 800.517324] [<ffff0000080b4838>] handle_hva_to_gpa+0xec/0x15c
[ 800.523063] [<ffff0000080b6c5c>] kvm_age_hva+0x5c/0xcc
[ 800.528194] [<ffff0000080a7c3c>] kvm_mmu_notifier_clear_flush_young+0x54/0x90
[ 800.535324] [<ffff00000827a0e8>] __mmu_notifier_clear_flush_young+0x6c/0xa8
[ 800.542279] [<ffff00000825a644>] page_referenced_one+0x1e0/0x1fc
[ 800.548279] [<ffff00000827e8f8>] rmap_walk_ksm+0x124/0x1a0
[ 800.553759] [<ffff00000825c974>] rmap_walk+0x94/0x98
[ 800.558717] [<ffff00000825ca98>] page_referenced+0x120/0x180
[ 800.564369] [<ffff000008228c58>] shrink_active_list+0x218/0x4a4
[ 800.570281] [<ffff000008229470>] shrink_node_memcg+0x58c/0x6fc
[ 800.576107] [<ffff0000082296c4>] shrink_node+0xe4/0x328
[ 800.581325] [<ffff000008229c9c>] do_try_to_free_pages+0xe4/0x3b8
[ 800.587324] [<ffff00000822a094>] try_to_free_pages+0x124/0x234
[ 800.593150] [<ffff000008216aa0>] __alloc_pages_nodemask+0x564/0xf7c
[ 800.599412] [<ffff000008292814>] khugepaged_alloc_page+0x38/0xb8
[ 800.605411] [<ffff0000082933bc>] collapse_huge_page+0x74/0xd70
[ 800.611238] [<ffff00000829470c>] khugepaged_scan_mm_slot+0x654/0xa98
[ 800.617585] [<ffff000008294e0c>] khugepaged+0x2bc/0x49c
[ 800.622803] [<ffff0000080ffb70>] kthread+0x124/0x150
[ 800.627762] [<ffff0000080849f0>] ret_from_fork+0x10/0x1c
[ 800.633066] ---[ end trace 944c130b5252fb01 ]---
-------------------------------------------------------------------------

The root cause might be: we can't guarantee that the parameter start and end
in handle_hva_to_gpa is PAGE_SIZE aligned, let alone hva_start and hva_end.
So why not aligning them the first place?
at the first place of handle_hva_to_gpa()?
but boundary check is needed in each loop of kvm_for_each_memslot. Am I missing
anything here?
This bug is introduced by commit 056aad67f836 ("kvm: arm/arm64: Rework gpa
callback handlers")

It fixes the bug by use pfn size converted.

Fixes: 056aad67f836 ("kvm: arm/arm64: Rework gpa callback handlers")

Signed-off-by: jia.he@xxxxxxxxxxxxxxxx
Signed-off-by: li.zhang@xxxxxxxxxxxxxxxx
---
virt/kvm/arm/mmu.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/virt/kvm/arm/mmu.c b/virt/kvm/arm/mmu.c
index 7f6a944..9dd7ae4 100644
--- a/virt/kvm/arm/mmu.c
+++ b/virt/kvm/arm/mmu.c
@@ -1744,7 +1744,7 @@ static int handle_hva_to_gpa(struct kvm *kvm,
/* we only care about the pages that the guest sees */
kvm_for_each_memslot(memslot, slots) {
unsigned long hva_start, hva_end;
- gfn_t gpa;
+ gpa_t gpa, gpa_end;
hva_start = max(start, memslot->userspace_addr);
hva_end = min(end, memslot->userspace_addr +
@@ -1753,7 +1753,9 @@ static int handle_hva_to_gpa(struct kvm *kvm,
continue;
gpa = hva_to_gfn_memslot(hva_start, memslot) << PAGE_SHIFT;
- ret |= handler(kvm, gpa, (u64)(hva_end - hva_start), data);
+ gpa_end = hva_to_gfn_memslot(hva_end + PAGE_SIZE - 1, memslot)
+ << PAGE_SHIFT;
+ ret |= handler(kvm, gpa, (u64)(gpa_end - gpa), data);
But we're looking for the mapping in the same memslot, so the distance
between hva and hva_end is the same as the one between gpa and gpa_end
if you didn't align it.
maybe not, sometimes hva_end-hva != gpa_end-gpa
start=fffdc37f0200,hva_start=fffdc37f0200,end=fffdc3800200,hva_end=fffdc3800000,gpa=3ff0000,gfn_end=4000000

but sometimes it is:
start=ffff60590200,hva_start=ffff60590200,end=ffff605a0200,hva_end=ffff605a0200,gpa=1fb190000,gfn_end=1fb1b0000
sorry , disordered above 2 cases for mistake (-_-)!
IMO, the unalignment is caused by the ksm stable page flag STABLE_FLAG. I will
propose another ksm patch to fix itã
But from handle_hva_to_gpa's point of view, arm kvm needs to void the followup
exception, just like what powerpc andx86 have done.

So why not align both start and end and skip the double lookup?

}
return ret;
@@ -1823,7 +1825,7 @@ static int kvm_age_hva_handler(struct kvm *kvm, gpa_t gpa, u64 size, void *data)
pmd_t *pmd;
pte_t *pte;
- WARN_ON(size != PAGE_SIZE && size != PMD_SIZE);
+ WARN_ON((size & ~PAGE_MASK) != 0);
pmd = stage2_get_pmd(kvm, NULL, gpa);
if (!pmd || pmd_none(*pmd)) /* Nothing there */
return 0;
@@ -1843,7 +1845,7 @@ static int kvm_test_age_hva_handler(struct kvm *kvm, gpa_t gpa, u64 size, void *
pmd_t *pmd;
pte_t *pte;
- WARN_ON(size != PAGE_SIZE && size != PMD_SIZE);
+ WARN_ON((size & ~PAGE_MASK) != 0);
pmd = stage2_get_pmd(kvm, NULL, gpa);
if (!pmd || pmd_none(*pmd)) /* Nothing there */
return 0;

I'll let Suzuki comment on this, but I'm a bit suspicious of this patch.
sure, more comments, more clear for the issue.


--
Cheers,
Jia