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    SubjectRe: [PATCH] arm64: KVM: VHE: save and restore some PSTATE bits
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    On 2017/9/6 20:30, Vladimir Murzin wrote:
    > On 06/09/17 13:14, gengdongjiu wrote:
    >>
    >>
    >> On 2017/9/6 20:00, Vladimir Murzin wrote:
    >>> On 06/09/17 11:35, gengdongjiu wrote:
    >>>> Vladimir,
    >>>>
    >>>> On 2017/9/6 17:41, Vladimir Murzin wrote:
    >>>>> Can you please elaborate on cases where PAN is not enabled?
    >>>>
    >>>> I mean the informal private usage, For example, he disabled the PAN dynamically to let kernel space to access the user space.
    >>>> After he dynamic disabled the PAN, then switched to guest OS. after return to host. he found the PAN stage is modified.
    >>>> Of cause this is not a formal usage, in our host kernel, it is always enabled, no dynamic change, but I means it may exist such cases.
    >>>>
    >>>>
    >>>
    >>> So, in short, there is no real issue with PAN, right? What about UAO?
    >> For the PAN, if host OS dynamically enable/disable PAN should have issue.
    >> Do you think that is not a issue as above description?
    >>
    >> "host OS dynamically disable the PAN, but after go back from the guest OS, The PAN is unexpectedly enabled"
    >
    > Do you see effect of "PAN is unexpectedly enabled"?
    In fact I did not encounter this case, but I think it can exist.
    I think if host OS dynamically disable PAN, it wants the host kernel access the user space address space not through copy_to/from_user API.
    Now if it is unexpectedly enabled, when host kernel still accesses the user space address, it will happen MMU fault exception.


    >
    > Cheers
    > Vladimir
    >
    >>
    >>>
    >>> Cheers
    >>> Vladimir
    >>>
    >>> .
    >>>
    >>
    >>
    >
    >
    > .
    >

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