From: Sean Christopherson <seanjc@google.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Nitesh Narayan Lal <nitesh@redhat.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Maxim Levitsky <mlevitsk@redhat.com>,
Eduardo Habkost <ehabkost@redhat.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 7/8] KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except()
Date: Thu, 2 Sep 2021 21:08:10 +0000 [thread overview]
Message-ID: <YTE9OsXABLzUitUd@google.com> (raw)
In-Reply-To: <20210827092516.1027264-8-vkuznets@redhat.com>
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@redhat.com>
> ---
> 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
>
next prev parent reply other threads:[~2021-09-02 21:08 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-27 9:25 [PATCH v4 0/8] KVM: Various fixes and improvements around kicking vCPUs Vitaly Kuznetsov
2021-08-27 9:25 ` [PATCH v4 1/8] KVM: Clean up benign vcpu->cpu data races when " Vitaly Kuznetsov
2021-08-27 9:25 ` [PATCH v4 2/8] KVM: KVM: Use cpumask_available() to check for NULL cpumask " Vitaly Kuznetsov
2021-08-27 9:25 ` [PATCH v4 3/8] KVM: x86: hyper-v: Avoid calling kvm_make_vcpus_request_mask() with vcpu_mask==NULL Vitaly Kuznetsov
2021-09-02 20:57 ` Sean Christopherson
2021-08-27 9:25 ` [PATCH v4 4/8] KVM: Optimize kvm_make_vcpus_request_mask() a bit Vitaly Kuznetsov
2021-09-02 21:00 ` Sean Christopherson
2021-08-27 9:25 ` [PATCH v4 5/8] KVM: Drop 'except' parameter from kvm_make_vcpus_request_mask() Vitaly Kuznetsov
2021-09-02 21:00 ` Sean Christopherson
2021-08-27 9:25 ` [PATCH v4 6/8] KVM: x86: Fix stack-out-of-bounds memory access from ioapic_write_indirect() Vitaly Kuznetsov
2021-08-27 9:25 ` [PATCH v4 7/8] KVM: Pre-allocate cpumasks for kvm_make_all_cpus_request_except() Vitaly Kuznetsov
2021-09-02 21:08 ` Sean Christopherson [this message]
2021-09-03 7:20 ` Vitaly Kuznetsov
2021-09-03 14:54 ` Sean Christopherson
2021-08-27 9:25 ` [PATCH v4 8/8] KVM: Make kvm_make_vcpus_request_mask() use pre-allocated cpu_kick_mask Vitaly Kuznetsov
2021-09-02 21:19 ` Sean Christopherson
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