RE: [PATCH v3 03/11] KVM: SVM: Change intercept_dr to generic intercepts

Babu Moger
2020-07-30T16:38:15Z

> -----Original Message-----
> From: Paolo Bonzini <pbonzini@redhat.com>
> Sent: Wednesday, July 29, 2020 6:12 PM
> To: Jim Mattson <jmattson@google.com>; Moger, Babu
> <Babu.Moger@amd.com>
> Cc: Vitaly Kuznetsov <vkuznets@redhat.com>; Wanpeng Li
> <wanpengli@tencent.com>; Sean Christopherson
> <sean.j.christopherson@intel.com>; kvm list <kvm@vger.kernel.org>; Joerg
> Roedel <joro@8bytes.org>; the arch/x86 maintainers <x86@kernel.org>; LKML
> <linux-kernel@vger.kernel.org>; Ingo Molnar <mingo@redhat.com>; Borislav
> Petkov <bp@alien8.de>; H . Peter Anvin <hpa@zytor.com>; Thomas Gleixner
> <tglx@linutronix.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