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    SubjectRE: [PATCH v3 1/3] x86/hyperv: Use slow_virt_to_phys() in page transition hypervisor callback
    Date
    From: Edgecombe, Rick P <rick.p.edgecombe@intel.com> Sent: Friday, January 12, 2024 9:17 AM
    >
    > On Fri, 2024-01-12 at 15:07 +0000, Michael Kelley wrote:
    > > The comment is Kirill Shutemov's suggestion based on comments in
    > > an earlier version of the patch series.  See [1].   The intent is to
    > > prevent
    > > some later revision to slow_virt_to_phys() from adding a check for
    > > the
    > > present bit and breaking the CoCo VM hypervisor callback.  Yes, the
    > > comment could get stale, but I'm not sure how else to call out the
    > > implicit dependency.  The idea of creating a private version of
    > > slow_virt_to_phys() for use only in the CoCo VM hypervisor callback
    > > is also discussed in the thread, but that seems worse overall.
    >
    > Well, it's not a huge deal, but I would have just put a comment at the
    > caller like:
    >
    > /*
    > * Use slow_virt_to_phys() instead of vmalloc_to_page(), because it
    > * returns the PFN even for NP PTEs.
    > */

    Yes, that comment is added in this patch.

    >
    > If someone is changing slow_virt_to_phys() they should check the
    > callers to make sure they won't break anything. They can see the
    > comment then and have an easy time.
    >
    > An optional comment at slow_virt_to_phys() could explain how the
    > function works in regards to the present bit, but not include details
    > about CoCoO VM page transition's usage of the present bit. The proposed
    > comment text looks like something more appropriate for a commit log.

    Kirill -- you originally asked for a comment in slow_virt_to_phys(). [1]
    Are you OK with Rick's proposal?

    Michael

    [1] https://lore.kernel.org/lkml/20230828221333.5blshosyqafbgwlc@box.shutemov.name/

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