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    SubjectRe: [PATCH v10 10/16] KVM: x86: Introduce KVM_GET_SHARED_PAGES_LIST ioctl
    On Wed, Feb 17, 2021, Kalra, Ashish wrote:
    > From: Sean Christopherson <seanjc@google.com>
    > On Thu, Feb 04, 2021, Ashish Kalra wrote:
    > > From: Brijesh Singh <brijesh.singh@amd.com>
    > >
    > > The ioctl is used to retrieve a guest's shared pages list.
    >
    > >What's the performance hit to boot time if KVM_HC_PAGE_ENC_STATUS is passed
    > >through to userspace? That way, userspace could manage the set of pages >in
    > >whatever data structure they want, and these get/set ioctls go away.
    >
    > What is the advantage of passing KVM_HC_PAGE_ENC_STATUS through to user-space
    > ?
    >
    > As such it is just a simple interface to get the shared page list via the
    > get/set ioctl's. simply an array is passed to these ioctl to get/set the
    > shared pages list.

    It eliminates any probability of the kernel choosing the wrong data structure,
    and it's two fewer ioctls to maintain and test.

    > >Also, aren't there plans for an in-guest migration helper? If so, do we
    > >have any idea what that interface will look like? E.g. if we're going to
    > >end up with a full >fledged driver in the guest, why not bite the bullet now
    > >and bypass KVM entirely?
    >
    > Even the in-guest migration helper will be using page encryption status
    > hypercalls, so some interface is surely required.

    If it's a driver with a more extensive interace, then the hypercalls can be
    replaced by a driver operation. That's obviously a big if, though.

    > Also the in-guest migration will be mainly an OVMF component, won't really
    > be a full fledged kernel driver in the guest.

    Is there code and/or a description of what the proposed helper would look like?

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