On Tue, Aug 23, 2022 at 10:26:09AM +0800, Chao Gao <chao.gao@xxxxxxxxx> wrote: > On Fri, Aug 19, 2022 at 11:00:09PM -0700, isaku.yamahata@xxxxxxxxx wrote: > >From: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> > > > >Because kvm_count_lock unnecessarily complicates the KVM locking convention > >Drop kvm_count_lock and instead protect kvm_usage_count with kvm_lock for > >simplicity. > > > >Opportunistically add some comments on locking. > > > >Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx> > >Signed-off-by: Isaku Yamahata <isaku.yamahata@xxxxxxxxx> > >--- > > static cpumask_var_t cpus_hardware_enabled; > >@@ -4999,6 +4998,8 @@ static void hardware_enable_nolock(void *junk) > > int cpu = raw_smp_processor_id(); > > int r; > > > >+ WARN_ON_ONCE(preemptible()); > >+ > > if (cpumask_test_cpu(cpu, cpus_hardware_enabled)) > > return; > > > >@@ -5015,10 +5016,10 @@ static void hardware_enable_nolock(void *junk) > > > > static int kvm_starting_cpu(unsigned int cpu) > > { > >- raw_spin_lock(&kvm_count_lock); > >+ mutex_lock(&kvm_lock); > > kvm_starting_cpu() is called with interrupt disabled. So we cannot use > sleeping locks (e.g., mutex) here. So your patch to move it to online section [1] is needed. I thought I can pullin only some of your patches. But whole your patches are needed. [1] https://lore.kernel.org/lkml/20220317091539.GA7257@gao-cwp/T/#mcc0fd81e7a19601e7c3ce451582c516d38f977f6 -- Isaku Yamahata <isaku.yamahata@xxxxxxxxx>