linux-kernel - Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

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Date:   Wed, 18 Dec 2019 16:58:57 -0500
From:   Peter Xu <peterx@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: Re: [PATCH RFC 04/15] KVM: Implement ring-based dirty memory tracking

On Tue, Dec 17, 2019 at 05:28:54PM +0100, Paolo Bonzini wrote:
> On 17/12/19 17:24, Peter Xu wrote:
> >> No, please pass it all the way down to the [&] functions but not to
> >> kvm_write_guest_page.  Those should keep using vcpu->kvm.
> > Actually I even wanted to refactor these helpers.  I mean, we have two
> > sets of helpers now, kvm_[vcpu]_{read|write}*(), so one set is per-vm,
> > the other set is per-vcpu.  IIUC the only difference of these two are
> > whether we should consider ((vcpu)->arch.hflags & HF_SMM_MASK) or we
> > just write to address space zero always.
> 
> Right.
> 
> > Could we unify them into a
> > single set of helper (I'll just drop the *_vcpu_* helpers because it's
> > longer when write) but we always pass in vcpu* as the first parameter?
> > Then we add another parameter "vcpu_smm" to show whether we want to
> > consider the HF_SMM_MASK flag.
> 
> You'd have to check through all KVM implementations whether you always
> have the vCPU.  Also non-x86 doesn't have address spaces, and by the
> time you add ", true" or ", false" it's longer than the "_vcpu_" you
> have removed.  So, not a good idea in my opinion. :D

Well, now I've changed my mind. :) (considering that we still have
many places that will not have vcpu*...)

I can simply add that "vcpu_smm" parameter to kvm_vcpu_write_*()
without removing the kvm_write_*() helpers.  Then I'll be able to
convert most of the kvm_write_*() (or its family) callers to
kvm_vcpu_write*(..., vcpu_smm=false) calls where proper.

Would that be good?

-- 
Peter Xu