linux-kernel - Re: [PATCH v5 8/8] KVM: Make kvm_make_vcpus_request_mask() use pre-allocated cpu_kick

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Date:   Fri, 3 Sep 2021 16:26:36 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>
Cc:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        "Dr. David Alan Gilbert" <dgilbert@...hat.com>,
        Nitesh Narayan Lal <nitesh@...hat.com>,
        Lai Jiangshan <jiangshanlai@...il.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 8/8] KVM: Make kvm_make_vcpus_request_mask() use
 pre-allocated cpu_kick_mask

On Fri, Sep 03, 2021, Vitaly Kuznetsov wrote:
> kvm_make_vcpus_request_mask() already disables preemption so just like
> kvm_make_all_cpus_request_except() it can be switched to using
> pre-allocated per-cpu cpumasks. This allows for improvements for both
> users of the function: in Hyper-V emulation code 'tlb_flush' can now be
> dropped from 'struct kvm_vcpu_hv' and kvm_make_scan_ioapic_request_mask()
> gets rid of dynamic allocation.
> 
> cpumask_available() checks in kvm_make_vcpu_request() and
> kvm_kick_many_cpus() can now be dropped as they checks for an impossible
> condition: kvm_init() makes sure per-cpu masks are allocated.
> 
> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---

Reviewed-by: Sean Christopherson <seanjc@...gle.com>

> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index a4752dcc2a75..91c1e6c98b0f 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -9224,14 +9224,8 @@ static void process_smi(struct kvm_vcpu *vcpu)
>  void kvm_make_scan_ioapic_request_mask(struct kvm *kvm,
>  				       unsigned long *vcpu_bitmap)
>  {
> -	cpumask_var_t cpus;
> -
> -	zalloc_cpumask_var(&cpus, GFP_ATOMIC);
> -
>  	kvm_make_vcpus_request_mask(kvm, KVM_REQ_SCAN_IOAPIC,
> -				    vcpu_bitmap, cpus);
> -
> -	free_cpumask_var(cpus);
> +				    vcpu_bitmap);

Nit, this can all go on a single line.

>  }
>  
>  void kvm_make_scan_ioapic_request(struct kvm *kvm)