linux-kernel - Re: [PATCH v2 2/3] KVM: X86: Implement PV sched yield hypercall

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Date:   Thu, 30 May 2019 09:09:52 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Liran Alon <liran.alon@...cle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH v2 2/3] KVM: X86: Implement PV sched yield hypercall

On Wed, 29 May 2019 at 20:28, Liran Alon <liran.alon@...cle.com> wrote:
>
>
>
> > On 28 May 2019, at 3:53, Wanpeng Li <kernellwp@...il.com> wrote:
> >
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > The target vCPUs are in runnable state after vcpu_kick and suitable
> > as a yield target. This patch implements the sched yield hypercall.
> >
> > 17% performace increase of ebizzy benchmark can be observed in an
> > over-subscribe environment. (w/ kvm-pv-tlb disabled, testing TLB flush
> > call-function IPI-many since call-function is not easy to be trigged
> > by userspace workload).
> >
> > Cc: Paolo Bonzini <pbonzini@...hat.com>
> > Cc: Radim Krčmář <rkrcmar@...hat.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > arch/x86/kvm/x86.c | 24 ++++++++++++++++++++++++
> > 1 file changed, 24 insertions(+)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index e7e57de..2ceef51 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -7172,6 +7172,26 @@ void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu)
> >       kvm_x86_ops->refresh_apicv_exec_ctrl(vcpu);
> > }
> >
> > +void kvm_sched_yield(struct kvm *kvm, u64 dest_id)
> > +{
> > +     struct kvm_vcpu *target;
> > +     struct kvm_apic_map *map;
> > +
> > +     rcu_read_lock();
> > +     map = rcu_dereference(kvm->arch.apic_map);
> > +
> > +     if (unlikely(!map))
> > +             goto out;
> > +
>
> We should have a bounds-check here on “dest_id”.

Yeah, fix it in v3.

Regards,
Wanpeng Li