On 09/05/17 15:22, David Gibson wrote: > On Tue, May 09, 2017 at 07:25:51AM +1000, Alexey Kardashevskiy wrote: >> On 09/05/17 06:17, Jose Ricardo Ziviani wrote: >>> This reverts commit 3dc410ae83e6cb76c81ea30a05d62596092b3165. >>> >>> Booting a radix guest in Power9 with that commit throws a host kernel >>> oops: >>> >>> [17582052553.360178] Unable to handle kernel paging request for data at >>> address 0xe64bb17da64ab078 >>> [17582052553.360420] Faulting instruction address: 0xc0000000002c3ddc >>> [17582052553.360533] Oops: Kernel access of bad area, sig: 11 [#1] >>> [17582052553.360643] SMP NR_CPUS=1024 >>> [17582052553.360645] NUMA >>> [17582052553.360712] PowerNV >>> [17582052553.360804] Modules linked in: vhost_net vhost tap xt_CHECKSUM >>> ipt_MASQUERADE nf_nat_masquerade_ipv4 ip6t_rpfilter ip6t_REJECT >>> nf_reject_ipv6 nf_conntrack_ipv6 nf_defrag_ipv6 xt_conntrack ip_set >>> nfnetlink ebtable_nat ebtable_broute bridge stp llc ip6table_mangle >>> ip6table_security ip6table_raw iptable_nat nf_conntrack_ipv4 nf_defrag_ipv4 >>> nf_nat_ipv4 nf_nat nf_conntrack libcrc32c iptable_mangle iptable_security >>> iptable_raw ebtable_filter ebtables ip6table_filter ip6_tables ses >>> enclosure scsi_transport_sas ipmi_powernv powernv_op_panel ipmi_devintf >>> ipmi_msghandler nfsd kvm_hv auth_rpcgss oid_registry nfs_acl lockd grace >>> sunrpc kvm tg3 ptp pps_core >>> [17582052553.361797] CPU: 5 PID: 4966 Comm: qemu-system-ppc Not tainted >>> 4.11.0-1.git4a6869a.el7.centos.ppc64le #1 >>> [17582052553.361972] task: c0000003c5e90a80 task.stack: c0000003c5f6c000 >>> [17582052553.362082] NIP: c0000000002c3ddc LR: c0000000002c3e80 CTR: >>> c0000000000ce2e0 >>> [17582052553.362214] REGS: c0000003c5f6f150 TRAP: 0380 Not tainted >>> (4.11.0-1.git4a6869a.el7.centos.ppc64le) >>> [17582052553.362467] MSR: 9000000000001031 <SF,HV,ME,IR,DR,LE> >>> [17582052553.362480] CR: 44008024 XER: 20000000 >>> [17582052553.362822] CFAR: c0000000002c3e7c SOFTE: 1 >>> [17582052553.362822] GPR00: 000000000000018f c0000003c5f6f3d0 >>> c00000000131fd00 0000000000000000 >>> [17582052553.362822] GPR04: 0000000000000005 00000000000001ff >>> 0000000000000000 7db04aa67db14ba6 >>> [17582052553.362822] GPR08: 264bb17da64ab000 e64bb17da64ab000 >>> 0000000000000078 0000000000000000 >>> [17582052553.362822] GPR12: c0000003bdb98008 c00000000fdc2d00 >>> c00000000000e148 0000000000000000 >>> [17582052553.362822] GPR16: 0000000008000000 0000000020000000 >>> 0000000000000000 c0000003c5f6f4c0 >>> [17582052553.362822] GPR20: c0000001ffff9440 c0000001fd033280 >>> c0000001fd0342a0 c0000001f24efff8 >>> [17582052553.362822] GPR24: 0000000000000200 00000001f24f0000 >>> 0000000000000010 0000000000020000 >>> [17582052553.362822] GPR28: 0800000000000000 00000001f24f0000 >>> 000000007db04aa6 00000000a64ab07d >>> [17582052553.365148] NIP [c0000000002c3ddc] vmalloc_to_page+0x19c/0x220 >>> [17582052553.365365] LR [c0000000002c3e80] vmalloc_to_pfn+0x20/0x50 >>> [17582052553.365582] Call Trace: >>> [17582052553.365720] [c0000003c5f6f3d0] [7265677368657265] >>> 0x7265677368657265 (unreliable) >>> [17582052553.365982] [c0000003c5f6f400] [c0000000002c3e80] >>> vmalloc_to_pfn+0x20/0x50 >>> [17582052553.366245] [c0000003c5f6f420] [c0000000000637e8] >>> vmalloc_to_phys+0x28/0x60 >>> [17582052553.366508] [c0000003c5f6f450] [c0000000000ce480] >>> kvmppc_rm_h_put_tce_indirect+0x1a0/0x540 >>> [17582052553.366812] [c0000003c5f6f590] [c0000000000d0314] >>> hcall_try_real_mode+0x60/0x7c >>> [17582052553.367074] [c0000003c5f6f600] [c0000000000cefac] >>> kvmppc_call_hv_entry+0x8/0x17c >>> [17582052553.367346] [c0000003c5f6f670] [c00800000375a970] >>> __kvmppc_vcore_entry+0x13c/0x1ac [kvm_hv] >>> [17582052553.367652] [c0000003c5f6f840] [c0080000037574a8] >>> kvmppc_run_core+0x788/0x1650 [kvm_hv] >>> [17582052553.367965] [c0000003c5f6fa00] [c0080000037590b8] >>> kvmppc_vcpu_run_hv+0x388/0x1200 [kvm_hv] >>> [17582052553.368287] [c0000003c5f6fb30] [c008000003274684] >>> kvmppc_vcpu_run+0x34/0x50 [kvm] >>> [17582052553.368558] [c0000003c5f6fb50] [c008000003270b54] >>> kvm_arch_vcpu_ioctl_run+0x114/0x2a0 [kvm] >>> [17582052553.368870] [c0000003c5f6fbd0] [c008000003263dd8] >>> kvm_vcpu_ioctl+0x5e8/0x7c0 [kvm] >>> [17582052553.369132] [c0000003c5f6fd40] [c000000000350b50] >>> do_vfs_ioctl+0xd0/0x8c0 >>> [17582052553.369395] [c0000003c5f6fde0] [c000000000351414] >>> SyS_ioctl+0xd4/0xf0 >>> [17582052553.369615] [c0000003c5f6fe30] [c00000000000b8e0] >>> system_call+0x38/0xfc >>> [17582052553.369875] Instruction dump: >>> [17582052553.370011] 53dfc42e 790807c6 394affff 7d08fb78 78638402 79081764 >>> 7d4a07b4 7c6a5038 >>> [17582052553.370281] 7908f5e6 7d094b78 794a1f24 38600000 <7d2a482a> >>> 7924cfe3 41820040 79260022 >>> [17582052553.370599] ---[ end trace 9470442ed18ae727 ]--- >>> >>> As soon as we identify and fix the issue that's causing such problem >>> I'll re-send the referred patch to re-enable TCE. > > This is a serious host kernel security bug. Modifying qemu not to > trigger it is not a fix; it's not even a workaround. > >> The proper fix is to change the host kernel to not advertise >> KVM_CAP_SPAPR_MULTITCE for radix guest. > > That doesn't sound like a fix either, though it might be part of one.
My point was that if a feature is known not to work, it should not be advertised rather than disabling the feature entirely in QEMU, even for the time being. vmalloc_to_pfn() needs a fix anyway. > What happens if qemu ignores what's advertised and tries to use the > multitce functions anyway? The point is you have an easy way for > userspace or a guest to crash the host kernel, which needs to be fixed > as a matter of urgency. Correct. > It's not clear to me why the multitce functions would break on radix > anyway. Isn't the TCE table format independent of the main MMU? It is from "rmap = (void *) vmalloc_to_phys(rmap);" to lock the page with TCEs in the H_PUT_TCE_INDIRECT handler, this is irrelevant to the TCE format. I am wondering why only this place fails though as vmalloc_to_phys() is used quite often, may be less on radix tree though. -- Alexey
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