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    SubjectRe: [PATCH 0/6] KVM: SVM: Wrap access to intercept masks into functions
    On Tue, Nov 30, 2010 at 12:42:28PM -0500, Avi Kivity wrote:
    > On 11/30/2010 07:03 PM, Joerg Roedel wrote:
    > > Hi Avi, Hi Marcelo,
    > >
    > > this patchset wraps the access to the intercept vectors in the VMCB into
    > > specific functions. There are two reasons for this:
    > >
    > > 1) In the nested-svm code the effective intercept masks are
    > > calculated from the host and the guest intercept masks.
    > > Whenever KVM changes the host intercept mask while the VCPU
    > > is in guest-mode the effective intercept masks need to be
    > > re-calculated. This is nicely wrapped into these functions
    > > now and makes the code more robust.
    > >
    > > 2) These changes make the implementation of the upcoming
    > > vmcb-clean-bits feature easier and also more robust (which
    > > was the main reason for writing this patchset).
    > >
    > > These patches were developed on-top of the patch-set I sent yesterday. I
    > > tested these patches with various guests (Windows-64, Linux 32,32e and
    > > 64 as well as with nested-svm).
    > >
    >
    > Looks good.
    >
    > One potential issue is that a series of set_intercept()s causes
    > recalc_intercepts() to be called multiple times. If it turns out to be
    > a problem, we can fix it by having an intercepts dirty bit and
    > recalculating during guest entry if the bit is set.
    >
    > Since it's nested svm only, I doubt we'll see a problem in the short term.

    Yes, we can optimize it if it turns out to be a problem. I thought that
    these changes happen infrequently enough and that there should be no
    more than 2-3 bits changed per exit-entry cycle at all.

    Joerg

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