[PATCH v5 7/8] KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()

From: Vitaly Kuznetsov
Date: Fri Sep 03 2021 - 03:52:45 EST


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 1238976ef614..ddd091f05c18 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 +5583,17 @@ 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))) {
+ r = -ENOMEM;
+ goto out_free_4;
+ }
+ }
+
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 +5619,10 @@ 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)
+ 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 +5642,12 @@ 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)
+ 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