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    SubjectRe: [Patch v4 05/13] init: Call mem_encrypt_init() after Hyper-V hypercall init is done
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    On 12/6/22 12:13 PM, Michael Kelley (LINUX) wrote:
    > From: Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@linux.intel.com>
    >>
    >>
    >>
    >> On 12/1/22 7:30 PM, Michael Kelley wrote:
    >>> Full Hyper-V initialization, including support for hypercalls, is done
    >>> as an apic_post_init callback via late_time_init(). mem_encrypt_init()
    >>> needs to make hypercalls when it marks swiotlb memory as decrypted.
    >>> But mem_encrypt_init() is currently called a few lines before
    >>> late_time_init(), so the hypercalls don't work.
    >>
    >> Did you consider moving hyper-v hypercall initialization before
    >> mem_encrypt_init(). Is there any dependency issue?
    >
    > Hyper-V initialization has historically been done using the callbacks
    > that exist in the x86 initialization paths, rather than adding explicit
    > Hyper-V init calls. As noted above, the full Hyper-V init is done on
    > the apic_post_init callback via late_time_init(). Conceivably we could
    > add an explicit call to do the Hyper-V init, but I think there's still a
    > problem in putting that Hyper-V init prior to the current location of
    > mem_encrypt_init(). I'd have to go check the history, but I think the
    > Hyper-V init needs to happen after the APIC is initialized.

    Ok. If there is a dependency or complexity issue, I recommend adding that
    detail in the commit log.

    >
    > It seems like moving mem_encrypt_init() slightly later is the cleaner
    > long-term solution. Are you aware of a likely problem arising in the
    > future with moving mem_encrypt_init()?

    I did not investigate in depth, but there appears to be no problem with
    moving mem_encrypt_init(). But my point is, if it is possible to fix this
    easily by changing Hyper-v specific initialization, we should consider it
    first before considering moving the common mem_encrypt_init() function.



    >
    > Michael
    >
    >>
    >>>
    >>> Fix this by moving mem_encrypt_init() after late_time_init() and
    >>> related clock initializations. The intervening initializations don't
    >>> do any I/O that requires the swiotlb, so moving mem_encrypt_init()
    >>> slightly later has no impact.
    >>>

    --
    Sathyanarayanan Kuppuswamy
    Linux Kernel Developer

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