From: Peter Xu Date: Thu, 16 Feb 2023 16:18:32 +0000 (+0800) Subject: kvm: dirty-ring: Fix race with vcpu creation X-Git-Tag: qemu-xen-4.18.0-rc5~232^2 X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=56adee407fc564da19e49cfe18e20e3da92320be;p=qemu-xen.git kvm: dirty-ring: Fix race with vcpu creation It's possible that we want to reap a dirty ring on a vcpu that is during creation, because the vcpu is put onto list (CPU_FOREACH visible) before initialization of the structures. In this case: qemu_init_vcpu x86_cpu_realizefn cpu_exec_realizefn cpu_list_add <---- can be probed by CPU_FOREACH qemu_init_vcpu cpus_accel->create_vcpu_thread(cpu); kvm_init_vcpu map kvm_dirty_gfns <--- kvm_dirty_gfns valid Don't try to reap dirty ring on vcpus during creation or it'll crash. Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2124756 Reported-by: Xiaohui Li Signed-off-by: Peter Xu Message-Id: <1d14deb6684bcb7de1c9633c5bd21113988cc698.1676563222.git.huangy81@chinatelecom.cn> Signed-off-by: Paolo Bonzini --- diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index f2a6ea6a68..cf3a88d90e 100644 --- a/accel/kvm/kvm-all.c +++ b/accel/kvm/kvm-all.c @@ -685,6 +685,15 @@ static uint32_t kvm_dirty_ring_reap_one(KVMState *s, CPUState *cpu) uint32_t ring_size = s->kvm_dirty_ring_size; uint32_t count = 0, fetch = cpu->kvm_fetch_index; + /* + * It's possible that we race with vcpu creation code where the vcpu is + * put onto the vcpus list but not yet initialized the dirty ring + * structures. If so, skip it. + */ + if (!cpu->created) { + return 0; + } + assert(dirty_gfns && ring_size); trace_kvm_dirty_ring_reap_vcpu(cpu->cpu_index);