On Fri, Aug 27, 2021, Vitaly Kuznetsov wrote:
> Allocating cpumask dynamically in zalloc_cpumask_var() is not ideal.
> Allocation is somewhat slow and can (in theory and when CPUMASK_OFFSTACK)
> fail. kvm_make_all_cpus_request_except() already disables preemption so
> we can use pre-allocated per-cpu cpumasks instead.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
> ---
> virt/kvm/kvm_main.c | 29 +++++++++++++++++++++++------
> 1 file changed, 23 insertions(+), 6 deletions(-)
>
> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> index 2e9927c4eb32..2f5fe4f54a51 100644
> --- a/virt/kvm/kvm_main.c
> +++ b/virt/kvm/kvm_main.c
> @@ -155,6 +155,8 @@ static void kvm_uevent_notify_change(unsigned int type, struct kvm *kvm);
> static unsigned long long kvm_createvm_count;
> static unsigned long long kvm_active_vms;
>
> +static DEFINE_PER_CPU(cpumask_var_t, cpu_kick_mask);
> +
> __weak void kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
> unsigned long start, unsigned long end)
> {
> @@ -323,14 +325,15 @@ bool kvm_make_all_cpus_request_except(struct kvm *kvm, unsigned int req,
> struct kvm_vcpu *except)
> {
> struct kvm_vcpu *vcpu;
> - cpumask_var_t cpus;
> + struct cpumask *cpus;
> bool called;
> int i, me;
>
> - zalloc_cpumask_var(&cpus, GFP_ATOMIC);
> -
> me = get_cpu();
>
> + cpus = this_cpu_cpumask_var_ptr(cpu_kick_mask);
> + cpumask_clear(cpus);
> +
> kvm_for_each_vcpu(i, vcpu, kvm) {
> if (vcpu == except)
> continue;
> @@ -340,7 +343,6 @@ bool kvm_make_all_cpus_request_except(struct kvm *kvm, unsigned int req,
> called = kvm_kick_many_cpus(cpus, !!(req & KVM_REQUEST_WAIT));
> put_cpu();
>
> - free_cpumask_var(cpus);
> return called;
> }
>
> @@ -5581,9 +5583,15 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
> goto out_free_3;
> }
>
> + for_each_possible_cpu(cpu) {
> + if (!alloc_cpumask_var_node(&per_cpu(cpu_kick_mask, cpu),
> + GFP_KERNEL, cpu_to_node(cpu)))
> + goto out_free_4;
'r' needs to be explicitly set to -EFAULT, e.g. in the current code it's
guaranteed to be 0 here.
> + }
> +
> r = kvm_async_pf_init();
> if (r)
> - goto out_free;
> + goto out_free_5;
>
> kvm_chardev_ops.owner = module;
> kvm_vm_fops.owner = module;
> @@ -5609,7 +5617,11 @@ int kvm_init(void *opaque, unsigned vcpu_size, unsigned vcpu_align,
>
> out_unreg:
> kvm_async_pf_deinit();
> -out_free:
> +out_free_5:
> + for_each_possible_cpu(cpu) {
Unnecessary braces.
> + free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
> + }
> +out_free_4:
> kmem_cache_destroy(kvm_vcpu_cache);
> out_free_3:
> unregister_reboot_notifier(&kvm_reboot_notifier);
> @@ -5629,8 +5641,13 @@ EXPORT_SYMBOL_GPL(kvm_init);
>
> void kvm_exit(void)
> {
> + int cpu;
> +
> debugfs_remove_recursive(kvm_debugfs_dir);
> misc_deregister(&kvm_dev);
> + for_each_possible_cpu(cpu) {
Same here.
> + free_cpumask_var(per_cpu(cpu_kick_mask, cpu));
> + }
> kmem_cache_destroy(kvm_vcpu_cache);
> kvm_async_pf_deinit();
> unregister_syscore_ops(&kvm_syscore_ops);
> --
> 2.31.1
>
