linux-kernel - RE: [PATCH v3 03/11] KVM: SVM: Change intercept

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Date:   Thu, 30 Jul 2020 11:38:06 -0500
From:   Babu Moger <babu.moger@....com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        Jim Mattson <jmattson@...gle.com>
Cc:     Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        kvm list <kvm@...r.kernel.org>, Joerg Roedel <joro@...tes.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RE: [PATCH v3 03/11] KVM: SVM: Change intercept_dr to generic
 intercepts



> -----Original Message-----
> From: Paolo Bonzini <pbonzini@...hat.com>
> Sent: Wednesday, July 29, 2020 6:12 PM
> To: Jim Mattson <jmattson@...gle.com>; Moger, Babu
> <Babu.Moger@....com>
> Cc: Vitaly Kuznetsov <vkuznets@...hat.com>; Wanpeng Li
> <wanpengli@...cent.com>; Sean Christopherson
> <sean.j.christopherson@...el.com>; kvm list <kvm@...r.kernel.org>; Joerg
> Roedel <joro@...tes.org>; the arch/x86 maintainers <x86@...nel.org>; LKML
> <linux-kernel@...r.kernel.org>; Ingo Molnar <mingo@...hat.com>; Borislav
> Petkov <bp@...en8.de>; H . Peter Anvin <hpa@...or.com>; Thomas Gleixner
> <tglx@...utronix.de>
> Subject: Re: [PATCH v3 03/11] KVM: SVM: Change intercept_dr to generic
> intercepts
> 
> On 29/07/20 01:59, Jim Mattson wrote:
> >>         case SVM_EXIT_READ_DR0 ... SVM_EXIT_WRITE_DR7: {
> >> -               u32 bit = 1U << (exit_code - SVM_EXIT_READ_DR0);
> >> -               if (svm->nested.ctl.intercept_dr & bit)
> >> +               if (__is_intercept(&svm->nested.ctl.intercepts,
> >> + exit_code))
> > Can I assume that all of these __<function> calls will become
> > <function> calls when the grand unification is done? (Maybe I should
> > just look ahead.)
> >
> 
> The <function> calls are reserved for the active VMCB while these take a vector.
> Probably it would be nicer to call them vmcb_{set,clr,is}_intercept and make
> them take a struct vmcb_control_area*, but apart from that the concept is fine
> 
> Once we do the vmcb01/vmcb02/vmcb12 work, there will not be anymore
> &svm->nested.ctl (replaced by &svm->nested.vmcb12->ctl) and we will be able
> to change them to take a struct vmcb*.  Then is_intercept would for example be
> simply:
Yea. True. It makes the code even cleaner. Also we can avoid calling
recalc_intercepts every time we set or clear a bit inside the same
function(like init_vmcb).

Let me try to understand.

vmcb01 is &svm->vmcb->control;l
vmcb02 is &svm->nested.hsave->control
vmcb12 is  &svm->nested.ctl;

The functions set_intercept and clr_intercept calls get_host_vmcb to get
the vmcb address.

static inline struct vmcb *get_host_vmcb(struct vcpu_svm *svm)
{
        if (is_guest_mode(&svm->vcpu))
                return svm->nested.hsave;
        else
                return svm->vmcb;
}

I need to study little bit when is_guest_mode Is on or off.  Let me take a
look at.

Thanks

> 
> 	return vmcb_is_intercept(svm->vmcb, nr);
> 
> as expected.
> 
> Paolo