Patch "KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()" has been added to the 5.10-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()

to the 5.10-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     kvm-pre-allocate-cpumasks-for-kvm_make_all_cpus_requ.patch
and it can be found in the queue-5.10 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 5478cdd8ade37304b8f56d7f27c006c57398e7f7
Author: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
Date:   Fri Sep 3 09:51:40 2021 +0200

    KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()
    
    [ Upstream commit baff59ccdc657d290be51b95b38ebe5de40036b4 ]
    
    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>
    Reviewed-by: Sean Christopherson <seanjc@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Message-Id: <20210903075141.403071-8-vkuznets@xxxxxxxxxx>
    Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
    Stable-dep-of: 2b0128127373 ("KVM: Register /dev/kvm as the _very_ last thing during initialization")
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 34931443dafac..d96a076aef0dd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -154,6 +154,8 @@ 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)
 {
@@ -327,14 +329,15 @@ 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;
@@ -344,7 +347,6 @@ 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;
 }
 
@@ -5002,9 +5004,17 @@ 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;
@@ -5030,7 +5040,10 @@ 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);
@@ -5050,8 +5063,12 @@ 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);