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

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Date:   Mon, 23 Jul 2018 14:10:59 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.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 Mon, 23 Jul 2018 at 14:00, Wanpeng Li <kernellwp@...il.com> 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.

Sorry, I think I mentioned "64 vCPUs per hypercall on 32-bit machines" above.

Regards,
Wanpeng Li

>
> 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();