linux-kernel - Re: [PATCH] KVM: X86: Do not yield to self

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Message-ID: <CANRm+CwC0RF-QZ40YSgSidQjGFK4NGxwjg3iLVSb2r=uEH=LCA@mail.gmail.com>
Date:   Fri, 9 Apr 2021 11:05:54 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: Re: [PATCH] KVM: X86: Do not yield to self

On Fri, 9 Apr 2021 at 00:56, Sean Christopherson <seanjc@...gle.com> wrote:
>
> On Thu, Apr 08, 2021, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > If the target is self we do not need to yield, we can avoid malicious
> > guest to play this.
> >
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> > Rebased on https://lore.kernel.org/kvm/1617697935-4158-1-git-send-email-wanpengli@tencent.com/
> >
> >  arch/x86/kvm/x86.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 43c9f9b..260650f 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -8230,6 +8230,10 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id)
> >       if (!target)
> >               goto no_yield;
> >
> > +     /* yield to self */
>
> If you're going to bother with a comment, maybe elaborate a bit, e.g.
>
>         /* Ignore requests to yield to self. */

Looks good, thanks.

    Wanpeng