4.15-stable review patch. If anyone has any objections, please let me know.
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From: Paul Mackerras paulus@ozlabs.org
commit 36ee41d161c67a6fcf696d4817a0da31f778938c upstream.
Running with CONFIG_DEBUG_ATOMIC_SLEEP reveals that HV KVM tries to read guest memory, in order to emulate guest instructions, while preempt is disabled and a vcore lock is held. This occurs in kvmppc_handle_exit_hv(), called from post_guest_process(), when emulating guest doorbell instructions on POWER9 systems, and also when checking whether we have hit a hypervisor breakpoint. Reading guest memory can cause a page fault and thus cause the task to sleep, so we need to avoid reading guest memory while holding a spinlock or when preempt is disabled.
To fix this, we move the preempt_enable() in kvmppc_run_core() to before the loop that calls post_guest_process() for each vcore that has just run, and we drop and re-take the vcore lock around the calls to kvmppc_emulate_debug_inst() and kvmppc_emulate_doorbell_instr().
Dropping the lock is safe with respect to the iteration over the runnable vcpus in post_guest_process(); for_each_runnable_thread is actually safe to use locklessly. It is possible for a vcpu to become runnable and add itself to the runnable_threads array (code near the beginning of kvmppc_run_vcpu()) and then get included in the iteration in post_guest_process despite the fact that it has not just run. This is benign because vcpu->arch.trap and vcpu->arch.ceded will be zero.
Fixes: 579006944e0d ("KVM: PPC: Book3S HV: Virtualize doorbell facility on POWER9") Signed-off-by: Paul Mackerras paulus@ozlabs.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/powerpc/kvm/book3s_hv.c | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
--- a/arch/powerpc/kvm/book3s_hv.c +++ b/arch/powerpc/kvm/book3s_hv.c @@ -1005,8 +1005,6 @@ static int kvmppc_emulate_doorbell_instr struct kvm *kvm = vcpu->kvm; struct kvm_vcpu *tvcpu;
- if (!cpu_has_feature(CPU_FTR_ARCH_300)) - return EMULATE_FAIL; if (kvmppc_get_last_inst(vcpu, INST_GENERIC, &inst) != EMULATE_DONE) return RESUME_GUEST; if (get_op(inst) != 31) @@ -1056,6 +1054,7 @@ static int kvmppc_emulate_doorbell_instr return RESUME_GUEST; }
+/* Called with vcpu->arch.vcore->lock held */ static int kvmppc_handle_exit_hv(struct kvm_run *run, struct kvm_vcpu *vcpu, struct task_struct *tsk) { @@ -1176,7 +1175,10 @@ static int kvmppc_handle_exit_hv(struct swab32(vcpu->arch.emul_inst) : vcpu->arch.emul_inst; if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) { + /* Need vcore unlocked to call kvmppc_get_last_inst */ + spin_unlock(&vcpu->arch.vcore->lock); r = kvmppc_emulate_debug_inst(run, vcpu); + spin_lock(&vcpu->arch.vcore->lock); } else { kvmppc_core_queue_program(vcpu, SRR1_PROGILL); r = RESUME_GUEST; @@ -1191,8 +1193,13 @@ static int kvmppc_handle_exit_hv(struct */ case BOOK3S_INTERRUPT_H_FAC_UNAVAIL: r = EMULATE_FAIL; - if ((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) + if (((vcpu->arch.hfscr >> 56) == FSCR_MSGP_LG) && + cpu_has_feature(CPU_FTR_ARCH_300)) { + /* Need vcore unlocked to call kvmppc_get_last_inst */ + spin_unlock(&vcpu->arch.vcore->lock); r = kvmppc_emulate_doorbell_instr(vcpu); + spin_lock(&vcpu->arch.vcore->lock); + } if (r == EMULATE_FAIL) { kvmppc_core_queue_program(vcpu, SRR1_PROGILL); r = RESUME_GUEST; @@ -2934,13 +2941,14 @@ static noinline void kvmppc_run_core(str /* make sure updates to secondary vcpu structs are visible now */ smp_mb();
+ preempt_enable(); + for (sub = 0; sub < core_info.n_subcores; ++sub) { pvc = core_info.vc[sub]; post_guest_process(pvc, pvc == vc); }
spin_lock(&vc->lock); - preempt_enable();
out: vc->vcore_state = VCORE_INACTIVE;