On Tue, 7 Apr 2020 09:52:53 +0200 Christian Borntraeger <borntraeger@xxxxxxxxxx> wrote: > On 07.04.20 09:49, David Hildenbrand wrote: > > On 07.04.20 09:33, Christian Borntraeger wrote: > >> > >> On 03.04.20 17:30, David Hildenbrand wrote: > >>> In case we have a region 1 ASCE, our shadow/g3 address can have > >>> any value. Unfortunately, (-1UL << 64) is undefined and triggers > >>> sometimes, rejecting valid shadow addresses when trying to walk > >>> our shadow table hierarchy. > >>> > >>> The result is that the prefix cannot get mapped and will loop > >>> basically forever trying to map it (-EAGAIN loop). > >>> > >>> After all, the broken check is only a sanity check, our table > >>> shadowing code in kvm_s390_shadow_tables() already checks these > >>> conditions, injecting proper translation exceptions. Turn it into > >>> a WARN_ON_ONCE(). > >> > >> After some testing I now triggered this warning: > >> > >> [ 541.633114] ------------[ cut here ]------------ > >> [ 541.633128] WARNING: CPU: 38 PID: 2812 at > >> arch/s390/mm/gmap.c:799 gmap_shadow_pgt_lookup+0x98/0x1a0 [ > >> 541.633129] Modules linked in: vhost_net vhost macvtap macvlan tap > >> kvm xt_CHECKSUM xt_MASQUERADE nf_nat_tftp nf_conntrack_tftp xt_CT > >> tun bridge stp llc xt_tcpudp ip6t_REJECT nf_reject_ipv6 > >> ip6t_rpfilter ipt_REJECT nf_reject_ipv4 xt_conntrack ip6table_nat > >> ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat > >> iptable_mangle iptable_raw iptable_security nf_conntrack > >> nf_defrag_ipv6 nf_defrag_ipv4 ip_set nfnetlink ip6table_filter > >> ip6_tables iptable_filter rpcrdma sunrpc rdma_ucm rdma_cm iw_cm > >> ib_cm configfs mlx5_ib s390_trng ghash_s390 prng aes_s390 > >> ib_uverbs des_s390 ib_core libdes sha3_512_s390 genwqe_card > >> sha3_256_s390 vfio_ccw crc_itu_t vfio_mdev sha512_s390 mdev > >> vfio_iommu_type1 sha1_s390 vfio eadm_sch zcrypt_cex4 sch_fq_codel > >> ip_tables x_tables mlx5_core sha256_s390 sha_common pkey zcrypt > >> rng_core autofs4 [ 541.633164] CPU: 38 PID: 2812 Comm: CPU 0/KVM > >> Not tainted 5.6.0+ #354 [ 541.633166] Hardware name: IBM 3906 M04 > >> 704 (LPAR) [ 541.633167] Krnl PSW : 0704d00180000000 > >> 00000014e05dc454 (gmap_shadow_pgt_lookup+0x9c/0x1a0) [ > >> 541.633169] R:0 T:1 IO:1 EX:1 Key:0 M:1 W:0 P:0 AS:3 > >> CC:1 PM:0 RI:0 EA:3 [ 541.633171] Krnl GPRS: 0000000000000000 > >> 0000001f00000000 0000001f487b8000 ffffffff80000000 [ 541.633172] > >> ffffffffffffffff 000003e003defa18 000003e003defa1c > >> 000003e003defa18 [ 541.633173] fffffffffffff000 > >> 000003e003defa18 000003e003defa28 0000001f70e06300 [ 541.633174] > >> 0000001f43484000 00000000043ed200 000003e003def978 > >> 000003e003def920 [ 541.633203] Krnl Code: 00000014e05dc448: > >> b9800038 ngr %r3,%r8 00000014e05dc44c: > >> a7840014 brc 8,00000014e05dc474 > >> #00000014e05dc450: af000000 mc 0,0 > >> >00000014e05dc454: a728fff5 > >> > lhi %r2,-11 > >> 00000014e05dc458: a7180000 > >> lhi %r1,0 00000014e05dc45c: b2fa0070 > >> niai 7,0 00000014e05dc460: 4010b04a > >> sth %r1,74(%r11) 00000014e05dc464: b9140022 > >> lgfr %r2,%r2 [ 541.633215] Call Trace: > >> [ 541.633218] [<00000014e05dc454>] > >> gmap_shadow_pgt_lookup+0x9c/0x1a0 [ 541.633257] > >> [<000003ff804c57d6>] kvm_s390_shadow_fault+0x66/0x1e8 [kvm] [ > >> 541.633265] [<000003ff804c72dc>] vsie_run+0x43c/0x710 [kvm] [ > >> 541.633273] [<000003ff804c85ca>] kvm_s390_handle_vsie+0x632/0x750 > >> [kvm] [ 541.633281] [<000003ff804c123c>] > >> kvm_s390_handle_b2+0x84/0x4e0 [kvm] [ 541.633289] > >> [<000003ff804b46b2>] kvm_handle_sie_intercept+0x172/0xcb8 [kvm] [ > >> 541.633297] [<000003ff804b18a8>] __vcpu_run+0x658/0xc90 [kvm] [ > >> 541.633305] [<000003ff804b2920>] > >> kvm_arch_vcpu_ioctl_run+0x248/0x858 [kvm] [ 541.633313] > >> [<000003ff8049d454>] kvm_vcpu_ioctl+0x284/0x7b0 [kvm] [ > >> 541.633316] [<00000014e087d5ae>] ksys_ioctl+0xae/0xe8 [ > >> 541.633318] [<00000014e087d652>] __s390x_sys_ioctl+0x2a/0x38 [ > >> 541.633323] [<00000014e0ff02a2>] system_call+0x2a6/0x2c8 [ > >> 541.633323] Last Breaking-Event-Address: [ 541.633334] > >> [<000003ff804983e0>] kvm_running_vcpu+0x3ea9ee997d8/0x3ea9ee99950 > >> [kvm] [ 541.633335] ---[ end trace f69b6021855ea189 ]--- > >> > >> > >> Unfortunately no dump at that point in time. > >> I have other tests which are clearly fixed by this patch, so we > >> should propbably go forward anyway. Question is, is this just > >> another bug we need to fix or is the assumption that somebody else > >> checked all conditions so we can warn false? > > > > Yeah, I think it is via > > > > kvm_s390_shadow_fault()->gmap_shadow_pgt_lookup()->gmap_table_walk() > > > > where we just peek if there is already something shadowed. If not, > > we go via the full kvm_s390_shadow_tables() path. > > > > So we could either do sanity checks in gmap_shadow_pgt_lookup(), or > > rather drop the WARN_ON_ONCE. I think the latter makes sense, now > > that we understood the problem. > > Ok, so I will drop the WARN_ON_ONCE and fixup the commit message. > with those fixes, you can also add: Reviewed-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
