4.13-stable review patch. If anyone has any objections, please let me know.
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From: Paul Mackerras paulus@ozlabs.org
commit 38c53af853069adf87181684370d7b8866d6387b upstream.
Commit 5e9859699aba ("KVM: PPC: Book3S HV: Outline of KVM-HV HPT resizing implementation", 2016-12-20) added code that tries to exclude any use or update of the hashed page table (HPT) while the HPT resizing code is iterating through all the entries in the HPT. It does this by taking the kvm->lock mutex, clearing the kvm->arch.hpte_setup_done flag and then sending an IPI to all CPUs in the host. The idea is that any VCPU task that tries to enter the guest will see that the hpte_setup_done flag is clear and therefore call kvmppc_hv_setup_htab_rma, which also takes the kvm->lock mutex and will therefore block until we release kvm->lock.
However, any VCPU that is already in the guest, or is handling a hypervisor page fault or hypercall, can re-enter the guest without rechecking the hpte_setup_done flag. The IPI will cause a guest exit of any VCPUs that are currently in the guest, but does not prevent those VCPU tasks from immediately re-entering the guest.
The result is that after resize_hpt_rehash_hpte() has made a HPTE absent, a hypervisor page fault can occur and make that HPTE present again. This includes updating the rmap array for the guest real page, meaning that we now have a pointer in the rmap array which connects with pointers in the old rev array but not the new rev array. In fact, if the HPT is being reduced in size, the pointer in the rmap array could point outside the bounds of the new rev array. If that happens, we can get a host crash later on such as this one:
[91652.628516] Unable to handle kernel paging request for data at address 0xd0000000157fb10c [91652.628668] Faulting instruction address: 0xc0000000000e2640 [91652.628736] Oops: Kernel access of bad area, sig: 11 [#1] [91652.628789] LE SMP NR_CPUS=1024 NUMA PowerNV [91652.628847] Modules linked in: binfmt_misc 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 i2c_opal ipmi_powernv ipmi_devintf i2c_core ipmi_msghandler powernv_op_panel nfsd auth_rpcgss oid_registry nfs_acl lockd grace sunrpc kvm_hv kvm_pr kvm scsi_dh_alua dm_service_time dm_multipath tg3 ptp pps_core [last unloaded: stap_552b612747aec2da355051e464fa72a1_14259] [91652.629566] CPU: 136 PID: 41315 Comm: CPU 21/KVM Tainted: G O 4.14.0-1.rc4.dev.gitb27fc5c.el7.centos.ppc64le #1 [91652.629684] task: c0000007a419e400 task.stack: c0000000028d8000 [91652.629750] NIP: c0000000000e2640 LR: d00000000c36e498 CTR: c0000000000e25f0 [91652.629829] REGS: c0000000028db5d0 TRAP: 0300 Tainted: G O (4.14.0-1.rc4.dev.gitb27fc5c.el7.centos.ppc64le) [91652.629932] MSR: 900000010280b033 <SF,HV,VEC,VSX,EE,FP,ME,IR,DR,RI,LE,TM[E]> CR: 44022422 XER: 00000000 [91652.630034] CFAR: d00000000c373f84 DAR: d0000000157fb10c DSISR: 40000000 SOFTE: 1 [91652.630034] GPR00: d00000000c36e498 c0000000028db850 c000000001403900 c0000007b7960000 [91652.630034] GPR04: d0000000117fb100 d000000007ab00d8 000000000033bb10 0000000000000000 [91652.630034] GPR08: fffffffffffffe7f 801001810073bb10 d00000000e440000 d00000000c373f70 [91652.630034] GPR12: c0000000000e25f0 c00000000fdb9400 f000000003b24680 0000000000000000 [91652.630034] GPR16: 00000000000004fb 00007ff7081a0000 00000000000ec91a 000000000033bb10 [91652.630034] GPR20: 0000000000010000 00000000001b1190 0000000000000001 0000000000010000 [91652.630034] GPR24: c0000007b7ab8038 d0000000117fb100 0000000ec91a1190 c000001e6a000000 [91652.630034] GPR28: 00000000033bb100 000000000073bb10 c0000007b7960000 d0000000157fb100 [91652.630735] NIP [c0000000000e2640] kvmppc_add_revmap_chain+0x50/0x120 [91652.630806] LR [d00000000c36e498] kvmppc_book3s_hv_page_fault+0xbb8/0xc40 [kvm_hv] [91652.630884] Call Trace: [91652.630913] [c0000000028db850] [c0000000028db8b0] 0xc0000000028db8b0 (unreliable) [91652.630996] [c0000000028db8b0] [d00000000c36e498] kvmppc_book3s_hv_page_fault+0xbb8/0xc40 [kvm_hv] [91652.631091] [c0000000028db9e0] [d00000000c36a078] kvmppc_vcpu_run_hv+0xdf8/0x1300 [kvm_hv] [91652.631179] [c0000000028dbb30] [d00000000c2248c4] kvmppc_vcpu_run+0x34/0x50 [kvm] [91652.631266] [c0000000028dbb50] [d00000000c220d54] kvm_arch_vcpu_ioctl_run+0x114/0x2a0 [kvm] [91652.631351] [c0000000028dbbd0] [d00000000c2139d8] kvm_vcpu_ioctl+0x598/0x7a0 [kvm] [91652.631433] [c0000000028dbd40] [c0000000003832e0] do_vfs_ioctl+0xd0/0x8c0 [91652.631501] [c0000000028dbde0] [c000000000383ba4] SyS_ioctl+0xd4/0x130 [91652.631569] [c0000000028dbe30] [c00000000000b8e0] system_call+0x58/0x6c [91652.631635] Instruction dump: [91652.631676] fba1ffe8 fbc1fff0 fbe1fff8 f8010010 f821ffa1 2fa70000 793d0020 e9432110 [91652.631814] 7bbf26e4 7c7e1b78 7feafa14 409e0094 <807f000c> 786326e4 7c6a1a14 93a40008 [91652.631959] ---[ end trace ac85ba6db72e5b2e ]---
To fix this, we tighten up the way that the hpte_setup_done flag is checked to ensure that it does provide the guarantee that the resizing code needs. In kvmppc_run_core(), we check the hpte_setup_done flag after disabling interrupts and refuse to enter the guest if it is clear (for a HPT guest). The code that checks hpte_setup_done and calls kvmppc_hv_setup_htab_rma() is moved from kvmppc_vcpu_run_hv() to a point inside the main loop in kvmppc_run_vcpu(), ensuring that we don't just spin endlessly calling kvmppc_run_core() while hpte_setup_done is clear, but instead have a chance to block on the kvm->lock mutex.
Finally we also check hpte_setup_done inside the region in kvmppc_book3s_hv_page_fault() where the HPTE is locked and we are about to update the HPTE, and bail out if it is clear. If another CPU is inside kvm_vm_ioctl_resize_hpt_commit) and has cleared hpte_setup_done, then we know that either we are looking at a HPTE that resize_hpt_rehash_hpte() has not yet processed, which is OK, or else we will see hpte_setup_done clear and refuse to update it, because of the full barrier formed by the unlock of the HPTE in resize_hpt_rehash_hpte() combined with the locking of the HPTE in kvmppc_book3s_hv_page_fault().
Fixes: 5e9859699aba ("KVM: PPC: Book3S HV: Outline of KVM-HV HPT resizing implementation") Reported-by: Satheesh Rajendran satheera@in.ibm.com Signed-off-by: Paul Mackerras paulus@ozlabs.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kvm/book3s_64_mmu_hv.c | 10 ++++++++++ arch/powerpc/kvm/book3s_hv.c | 29 +++++++++++++++++++---------- 2 files changed, 29 insertions(+), 10 deletions(-)
--- a/arch/powerpc/kvm/book3s_64_mmu_hv.c +++ b/arch/powerpc/kvm/book3s_64_mmu_hv.c @@ -645,6 +645,16 @@ int kvmppc_book3s_hv_page_fault(struct k hnow_v = hpte_new_to_old_v(hnow_v, hnow_r); hnow_r = hpte_new_to_old_r(hnow_r); } + + /* + * If the HPT is being resized, don't update the HPTE, + * instead let the guest retry after the resize operation is complete. + * The synchronization for hpte_setup_done test vs. set is provided + * by the HPTE lock. + */ + if (!kvm->arch.hpte_setup_done) + goto out_unlock; + if ((hnow_v & ~HPTE_V_HVLOCK) != hpte[0] || hnow_r != hpte[1] || rev->guest_rpte != hpte[2]) /* HPTE has been changed under us; let the guest retry */ --- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -2688,11 +2688,14 @@ static noinline void kvmppc_run_core(str * Hard-disable interrupts, and check resched flag and signals. * If we need to reschedule or deliver a signal, clean up * and return without going into the guest(s). + * If the hpte_setup_done flag has been cleared, don't go into the + * guest because that means a HPT resize operation is in progress. */ local_irq_disable(); hard_irq_disable(); if (lazy_irq_pending() || need_resched() || - recheck_signals(&core_info)) { + recheck_signals(&core_info) || + (!kvm_is_radix(vc->kvm) && !vc->kvm->arch.hpte_setup_done)) { local_irq_enable(); vc->vcore_state = VCORE_INACTIVE; /* Unlock all except the primary vcore */ @@ -3061,7 +3064,7 @@ out:
static int kvmppc_run_vcpu(struct kvm_run *kvm_run, struct kvm_vcpu *vcpu) { - int n_ceded, i; + int n_ceded, i, r; struct kvmppc_vcore *vc; struct kvm_vcpu *v;
@@ -3115,6 +3118,20 @@ static int kvmppc_run_vcpu(struct kvm_ru
while (vcpu->arch.state == KVMPPC_VCPU_RUNNABLE && !signal_pending(current)) { + /* See if the HPT and VRMA are ready to go */ + if (!kvm_is_radix(vcpu->kvm) && + !vcpu->kvm->arch.hpte_setup_done) { + spin_unlock(&vc->lock); + r = kvmppc_hv_setup_htab_rma(vcpu); + spin_lock(&vc->lock); + if (r) { + kvm_run->exit_reason = KVM_EXIT_FAIL_ENTRY; + kvm_run->fail_entry.hardware_entry_failure_reason = 0; + vcpu->arch.ret = r; + break; + } + } + if (vc->vcore_state == VCORE_PREEMPT && vc->runner == NULL) kvmppc_vcore_end_preempt(vc);
@@ -3232,13 +3249,6 @@ static int kvmppc_vcpu_run_hv(struct kvm /* Order vcpus_running vs. hpte_setup_done, see kvmppc_alloc_reset_hpt */ smp_mb();
- /* On the first time here, set up HTAB and VRMA */ - if (!kvm_is_radix(vcpu->kvm) && !vcpu->kvm->arch.hpte_setup_done) { - r = kvmppc_hv_setup_htab_rma(vcpu); - if (r) - goto out; - } - flush_all_to_thread(current);
/* Save userspace EBB and other register values */ @@ -3286,7 +3296,6 @@ static int kvmppc_vcpu_run_hv(struct kvm } mtspr(SPRN_VRSAVE, user_vrsave);
- out: vcpu->arch.state = KVMPPC_VCPU_NOTREADY; atomic_dec(&vcpu->kvm->arch.vcpus_running); return r;