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    SubjectRe: [RFC PATCH 00/13] x86 User Interrupts support
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    On 10/1/2021 1:19 AM, Pavel Machek wrote:
    > Hi!
    >

    Thank you for reviewing the patches!

    >> Instructions
    >> ------------
    >> senduipi <index> - send a user IPI to a target task based on the UITT index.
    >>
    >> clui - Mask user interrupts by clearing UIF (User Interrupt Flag).
    >>
    >> stui - Unmask user interrupts by setting UIF.
    >>
    >> testui - Test current value of UIF.
    >>
    >> uiret - return from a user interrupt handler.
    >
    > Are other CPU vendors allowed to implement compatible instructions?
    >
    > If not, we should probably have VDSO entries so kernel can abstract
    > differences between CPUs.
    >

    Yes, we are evaluating VDSO support for this.

    >> Untrusted processes
    >> -------------------
    >> The current implementation expects only trusted and cooperating processes to
    >> communicate using user interrupts. Coordination is expected between processes
    >> for a connection teardown. In situations where coordination doesn't happen
    >> (say, due to abrupt process exit), the kernel would end up keeping shared
    >> resources (like UPID) allocated to avoid faults.
    >
    > Keeping resources allocated after process exit is a no-no.
    >

    I meant the resource is still tracked via the shared file descriptor, so
    it will eventually get freed when the FD release happens. I am planning
    to include better documentation on lifetime rules of these shared
    resources next time.

    Thanks,
    Sohil

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