linux-kernel - Re: [PATCH v4 4/6] KVM: X86: Implement PV IPIs send hypercall

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Message-ID: <e9037977-b6e6-b807-f9e5-8acaacb00f26@redhat.com>
Date:   Mon, 23 Jul 2018 08:09:21 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Wanpeng Li <kernellwp@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Radim Krcmar <rkrcmar@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH v4 4/6] KVM: X86: Implement PV IPIs send hypercall

On 23/07/2018 08:00, Wanpeng Li wrote:
> On Mon, 23 Jul 2018 at 13:52, Paolo Bonzini <pbonzini@...hat.com> wrote:
>>
>> On 20/07/2018 18:28, Wanpeng Li wrote:
>>> +a0: ipi_bitmap low 64 bits
>>> +a1: ipi_bitmap high 64 bits
>>> +a2: the lowest APIC ID in bitmap
>>> +a3: APIC ICR
>>> +
>>> +The hypercall lets a guest send multicast IPIs at most can handle
>>> +128 vCPUs per hypercall on 64-bit machines and 64 vCPUs per hypercall
>>> +on 32-bit machines.
>>> +
>>> +Returns 0 if successfully delivery the IPIs and 1 if discarded.
>>
>> This description does not mention what happens in 32-bit mode.
> 
> Will do in next version.
> 
>>
>>> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
>>> index 2b812b3..016c7e2 100644
>>> --- a/arch/x86/kvm/x86.c
>>> +++ b/arch/x86/kvm/x86.c
>>> @@ -6691,6 +6691,41 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid)
>>>       kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL);
>>>  }
>>>
>>> +/*
>>> + * Return 0 if successfully added and 1 if discarded.
>>> + */
>>> +static int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low,
>>> +             unsigned long ipi_bitmap_high, int min, int vector, int op_64_bit)
>>> +{
>>> +     int i;
>>> +     struct kvm_apic_map *map;
>>> +     struct kvm_vcpu *vcpu;
>>> +     struct kvm_lapic_irq irq = {
>>> +             .delivery_mode = APIC_DM_FIXED,
>>> +             .vector = vector,
>>> +     };
>>> +
>>> +     rcu_read_lock();
>>> +     map = rcu_dereference(kvm->arch.apic_map);
>>> +
>>> +     for_each_set_bit(i, &ipi_bitmap_low, BITS_PER_LONG) {
>>> +             vcpu = map->phys_map[min + i]->vcpu;
>>> +             if (!kvm_apic_set_irq(vcpu, &irq, NULL))
>>> +                     return 1;
>>> +     }
>>> +
>>> +     if (op_64_bit) {
>>> +             for_each_set_bit(i, &ipi_bitmap_high, BITS_PER_LONG) {
>>> +                     vcpu = map->phys_map[min + i + BITS_PER_LONG]->vcpu;
>>> +                     if (!kvm_apic_set_irq(vcpu, &irq, NULL))
>>> +                             return 1;
>>> +             }
>>> +     }
>>
>> The second loop processes the second argument, and it should always run,
>> even in 32-bit mode.  However, the phys_map index should be min + i + 32
>> in 32-bit mode and min + i + 64 in 64-bit mode.  (Using BITS_PER_LONG in
>> the for_each_set_bit length is not a bug instead; you could write it
>> explicitly as 32 in 32-bit mode, and 64 in 64-bit mode, but I think it's
>> a little bit more efficient if it's constant).
> 
> Good catch, below should fix it.
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index c9dbc2c..c118040 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -6701,6 +6701,7 @@ static int kvm_pv_send_ipi(struct kvm *kvm,
> unsigned long ipi_bitmap_low,
>      struct kvm_apic_map *map;
>      struct kvm_vcpu *vcpu;
>      struct kvm_lapic_irq irq = {0};
> +    int cluster_size = op_64_bit ? 64 : 32;
> 
>      switch (icr & APIC_VECTOR_MASK) {
>      default:
> @@ -6714,18 +6715,16 @@ static int kvm_pv_send_ipi(struct kvm *kvm,
> unsigned long ipi_bitmap_low,
>      rcu_read_lock();
>      map = rcu_dereference(kvm->arch.apic_map);
> 
> -    for_each_set_bit(i, &ipi_bitmap_low, BITS_PER_LONG) {
> +    for_each_set_bit(i, &ipi_bitmap_low, cluster_size) {
>          vcpu = map->phys_map[min + i]->vcpu;
>          if (!kvm_apic_set_irq(vcpu, &irq, NULL))
>              return 1;
>      }
> 
> -    if (op_64_bit) {
> -        for_each_set_bit(i, &ipi_bitmap_high, BITS_PER_LONG) {
> -            vcpu = map->phys_map[min + i + BITS_PER_LONG]->vcpu;
> -            if (!kvm_apic_set_irq(vcpu, &irq, NULL))
> -                return 1;
> -        }
> +    for_each_set_bit(i, &ipi_bitmap_high, cluster_size) {
> +        vcpu = map->phys_map[min + i + cluster_size]->vcpu;
> +        if (!kvm_apic_set_irq(vcpu, &irq, NULL))
> +            return 1;
>      }
> 
>      rcu_read_unlock();
> 

Yes, that should work.  Thanks!

Paolo