linux-kernel - Re: [PATCH v3 2/5] KVM: X86: Introduce need_cancel_enter

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Message-ID: <CANRm+CxfYB9TULkZdnUVyhFgLLWBScDXFRBrFo0Nig_H0VH_1w@mail.gmail.com>
Date:   Tue, 28 Apr 2020 15:17:30 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Sean Christopherson <sean.j.christopherson@...el.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>,
        Haiwei Li <lihaiwei@...cent.com>
Subject: Re: [PATCH v3 2/5] KVM: X86: Introduce need_cancel_enter_guest helper

On Tue, 28 Apr 2020 at 02:30, Sean Christopherson
<sean.j.christopherson@...el.com> wrote:
>
> On Fri, Apr 24, 2020 at 02:22:41PM +0800, Wanpeng Li wrote:
> > From: Wanpeng Li <wanpengli@...cent.com>
> >
> > Introduce need_cancel_enter_guest() helper, we need to check some
> > conditions before doing CONT_RUN, in addition, it can also catch
> > the case vmexit occurred while another event was being delivered
> > to guest software since vmx_complete_interrupts() adds the request
> > bit.
> >
> > Tested-by: Haiwei Li <lihaiwei@...cent.com>
> > Cc: Haiwei Li <lihaiwei@...cent.com>
> > Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
> > ---
> >  arch/x86/kvm/vmx/vmx.c | 12 +++++++-----
> >  arch/x86/kvm/x86.c     | 10 ++++++++--
> >  arch/x86/kvm/x86.h     |  1 +
> >  3 files changed, 16 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> > index f1f6638..5c21027 100644
> > --- a/arch/x86/kvm/vmx/vmx.c
> > +++ b/arch/x86/kvm/vmx/vmx.c
> > @@ -6577,7 +6577,7 @@ bool __vmx_vcpu_run(struct vcpu_vmx *vmx, unsigned long *regs, bool launched);
> >
> >  static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >  {
> > -     enum exit_fastpath_completion exit_fastpath;
> > +     enum exit_fastpath_completion exit_fastpath = EXIT_FASTPATH_NONE;
> >       struct vcpu_vmx *vmx = to_vmx(vcpu);
> >       unsigned long cr3, cr4;
> >
> > @@ -6754,10 +6754,12 @@ static enum exit_fastpath_completion vmx_vcpu_run(struct kvm_vcpu *vcpu)
> >       vmx_recover_nmi_blocking(vmx);
> >       vmx_complete_interrupts(vmx);
> >
> > -     exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
> > -     /* static call is better with retpolines */
> > -     if (exit_fastpath == EXIT_FASTPATH_CONT_RUN)
> > -             goto cont_run;
> > +     if (!kvm_need_cancel_enter_guest(vcpu)) {
> > +             exit_fastpath = vmx_exit_handlers_fastpath(vcpu);
> > +             /* static call is better with retpolines */
> > +             if (exit_fastpath == EXIT_FASTPATH_CONT_RUN)
> > +                     goto cont_run;
> > +     }
> >
> >       return exit_fastpath;
> >  }
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index 59958ce..4561104 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1581,6 +1581,13 @@ int kvm_emulate_wrmsr(struct kvm_vcpu *vcpu)
> >  }
> >  EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
> >
> > +bool kvm_need_cancel_enter_guest(struct kvm_vcpu *vcpu)
>
> What about kvm_vcpu_<???>_pending()?  Not sure what a good ??? would be.
> The "cancel_enter_guest" wording is a bit confusing when this is called
> from the VM-Exit path.
>
> > +{
> > +     return (vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu)
> > +         || need_resched() || signal_pending(current));
>
> Parantheses around the whole statement are unnecessary.  Personal preference
> is to put the || before the newline.

Handle the comments in v4.

    Wanpeng