KVM: use modern cpumask primitives, no cpumask_t on stack

We're getting rid on on-stack cpumasks for large NR_CPUS.

1) Use cpumask_var_t/alloc_cpumask_var.
2) smp_call_function_mask -> smp_call_function_many
3) cpus_clear, cpus_empty, cpu_set -> cpumask_clear, cpumask_empty,
   cpumask_set_cpu.

This actually generates slightly smaller code than the old one with
CONFIG_CPUMASKS_OFFSTACK=n.  (gcc knows that cpus cannot be NULL in
that case, where cpumask_var_t is cpumask_t[1]).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: Avi Kivity <avi@redhat.com>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index ba4275d..2d6ca79 100644 (file)
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -555,12 +555,14 @@ static void ack_flush(void *_completed)
 static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
 {
        int i, cpu, me;
-       cpumask_t cpus;
-       bool called = false;
+       cpumask_var_t cpus;
+       bool called = true;
        struct kvm_vcpu *vcpu;
 
+       if (alloc_cpumask_var(&cpus, GFP_ATOMIC))
+               cpumask_clear(cpus);
+
        me = get_cpu();
-       cpus_clear(cpus);
        for (i = 0; i < KVM_MAX_VCPUS; ++i) {
                vcpu = kvm->vcpus[i];
                if (!vcpu)
@@ -568,14 +570,17 @@ static bool make_all_cpus_request(struct kvm *kvm, unsigned int req)
                if (test_and_set_bit(req, &vcpu->requests))
                        continue;
                cpu = vcpu->cpu;
-               if (cpu != -1 && cpu != me)
-                       cpu_set(cpu, cpus);
-       }
-       if (!cpus_empty(cpus)) {
-               smp_call_function_mask(cpus, ack_flush, NULL, 1);
-               called = true;
+               if (cpus != NULL && cpu != -1 && cpu != me)
+                       cpumask_set_cpu(cpu, cpus);
        }
+       if (unlikely(cpus == NULL))
+               smp_call_function_many(cpu_online_mask, ack_flush, NULL, 1);
+       else if (!cpumask_empty(cpus))
+               smp_call_function_many(cpus, ack_flush, NULL, 1);
+       else
+               called = false;
        put_cpu();
+       free_cpumask_var(cpus);
        return called;
 }