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    SubjectRe: [RFC] /dev/ioasid uAPI proposal
    Date
    On 04/06/21 18:03, Jason Gunthorpe wrote:
    > On Fri, Jun 04, 2021 at 05:57:19PM +0200, Paolo Bonzini wrote:
    >> I don't want a security proof myself; I want to trust VFIO to make the right
    >> judgment and I'm happy to defer to it (via the KVM-VFIO device).
    >>
    >> Given how KVM is just a device driver inside Linux, VMs should be a slightly
    >> more roundabout way to do stuff that is accessible to bare metal; not a way
    >> to gain extra privilege.
    >
    > Okay, fine, lets turn the question on its head then.
    >
    > VFIO should provide a IOCTL VFIO_EXECUTE_WBINVD so that userspace VFIO
    > application can make use of no-snoop optimizations. The ability of KVM
    > to execute wbinvd should be tied to the ability of that IOCTL to run
    > in a normal process context.
    >
    > So, under what conditions do we want to allow VFIO to giave a process
    > elevated access to the CPU:

    Ok, I would definitely not want to tie it *only* to CAP_SYS_RAWIO (i.e.
    #2+#3 would be worse than what we have today), but IIUC the proposal
    (was it yours or Kevin's?) was to keep #2 and add #1 with an
    enable/disable ioctl, which then would be on VFIO and not on KVM. I
    assumed Alex was more or less okay with it, given he included me in the
    discussion.

    If later y'all switch to "it's always okay to issue the enable/disable
    ioctl", I guess the rationale would be documented in the commit message.

    Paolo

    >>> 1) User has access to a device that can issue no-snoop TLPS
    >>> 2) User has access to an IOMMU that can not block no-snoop (today)
    >>> 3) Require CAP_SYS_RAW_IO
    >>> 4) Anyone
    >
    > Jason
    >

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