On Fri, 2017-06-30 at 16:59 +1000, Paul Mackerras wrote:
> This fixes a typo where the wrong loop index was used to index
> the kvmppc_xive_vcpu.queues[] array in xive_pre_save_scan().
> The variable i contains the vcpu number; we need to index queues[]
> using j, which iterates from 0 to KVMPPC_XIVE_Q_COUNT-1.
>
> The effect of this bug is that things that save the interrupt
> controller state, such as "virsh dump", on a VM with more than
> 8 vCPUs, result in xive_pre_save_queue() getting called on a
> bogus queue structure, usually resulting in a crash like this:
>
> [ 501.821107] Unable to handle kernel paging request for data at address 0x00000084
> [ 501.821212] Faulting instruction address: 0xc008000004c7c6f8
> [ 501.821234] Oops: Kernel access of bad area, sig: 11 [#1]
> [ 501.821305] SMP NR_CPUS=1024
> [ 501.821307] NUMA
> [ 501.821376] PowerNV
> [ 501.821470] 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 ipmi_devintf ipmi_msghandler powernv_op_panel kvm_hv nfsd auth_rpcgss oid_registry nfs_acl lockd grace sunrpc kvm tg3 ptp pps_core
> [ 501.822477] CPU: 3 PID: 3934 Comm: live_migration Not tainted 4.11.0-4.git8caa70f.el7.centos.ppc64le #1
> [ 501.822633] task: c0000003f9e3ae80 task.stack: c0000003f9ed4000
> [ 501.822745] NIP: c008000004c7c6f8 LR: c008000004c7c628 CTR: 0000000030058018
> [ 501.822877] REGS: c0000003f9ed7980 TRAP: 0300 Not tainted (4.11.0-4.git8caa70f.el7.centos.ppc64le)
> [ 501.823030] MSR: 9000000000009033 <SF,HV,EE,ME,IR,DR,RI,LE>
> [ 501.823047] CR: 28022244 XER: 00000000
> [ 501.823203] CFAR: c008000004c7c77c DAR: 0000000000000084 DSISR: 40000000 SOFTE: 1
> [ 501.823203] GPR00: c008000004c7c628 c0000003f9ed7c00 c008000004c91450 00000000000000ff
> [ 501.823203] GPR04: c0000003f5580000 c0000003f559bf98 9000000000009033 0000000000000000
> [ 501.823203] GPR08: 0000000000000084 0000000000000000 00000000000001e0 9000000000001003
> [ 501.823203] GPR12: c00000000008a7d0 c00000000fdc1b00 000000000a9a0000 0000000000000000
> [ 501.823203] GPR16: 00000000402954e8 000000000a9a0000 0000000000000004 0000000000000000
> [ 501.823203] GPR20: 0000000000000008 c000000002e8f180 c000000002e8f1e0 0000000000000001
> [ 501.823203] GPR24: 0000000000000008 c0000003f5580008 c0000003f4564018 c000000002e8f1e8
> [ 501.823203] GPR28: 00003ff6e58bdc28 c0000003f4564000 0000000000000000 0000000000000000
> [ 501.825441] NIP [c008000004c7c6f8] xive_get_attr+0x3b8/0x5b0 [kvm]
> [ 501.825671] LR [c008000004c7c628] xive_get_attr+0x2e8/0x5b0 [kvm]
> [ 501.825887] Call Trace:
> [ 501.825991] [c0000003f9ed7c00] [c008000004c7c628] xive_get_attr+0x2e8/0x5b0 [kvm] (unreliable)
> [ 501.826312] [c0000003f9ed7cd0] [c008000004c62ec4] kvm_device_ioctl_attr+0x64/0xa0 [kvm]
> [ 501.826581] [c0000003f9ed7d20] [c008000004c62fcc] kvm_device_ioctl+0xcc/0xf0 [kvm]
> [ 501.826843] [c0000003f9ed7d40] [c000000000350c70] do_vfs_ioctl+0xd0/0x8c0
> [ 501.827060] [c0000003f9ed7de0] [c000000000351534] SyS_ioctl+0xd4/0xf0
> [ 501.827282] [c0000003f9ed7e30] [c00000000000b8e0] system_call+0x38/0xfc
> [ 501.827496] Instruction dump:
> [ 501.827632] 419e0078 3b760008 e9160008 83fb000c 83db0010 80fb0008 2f280000 60000000
> [ 501.827901] 60000000 60420000 419a0050 7be91764 <7d284c2c> 552a0ffe 7f8af040 419e003c
> [ 501.828176] ---[ end trace 2d0529a5bbbbafed ]---
>
> Signed-off-by: Paul Mackerras <paulus@xxxxxxxxxx>
Acked-by: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
> ---
> arch/powerpc/kvm/book3s_xive.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c
> index ffe1da95033a..08b200a0bbce 100644
> --- a/arch/powerpc/kvm/book3s_xive.c
> +++ b/arch/powerpc/kvm/book3s_xive.c
> @@ -1257,8 +1257,8 @@ static void xive_pre_save_scan(struct kvmppc_xive *xive)
> if (!xc)
> continue;
> for (j = 0; j < KVMPPC_XIVE_Q_COUNT; j++) {
> - if (xc->queues[i].qpage)
> - xive_pre_save_queue(xive, &xc->queues[i]);
> + if (xc->queues[j].qpage)
> + xive_pre_save_queue(xive, &xc->queues[j]);
> }
> }
>
