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    SubjectRe: [KVM PATCH v8 3/3] KVM: add iosignalfd support
    On Tue, Jun 23, 2009 at 12:57:53PM +0300, Avi Kivity wrote:
    > On 06/23/2009 11:56 AM, Michael S. Tsirkin wrote:
    >> On Thu, Jun 18, 2009 at 08:30:46PM -0400, Gregory Haskins wrote:
    >>
    >>> +static int
    >>> +iosignalfd_group_in_range(struct kvm_io_device *this, gpa_t addr, int len,
    >>> + int is_write)
    >>> +{
    >>> + struct _iosignalfd_group *p = to_group(this);
    >>> +
    >>> + return ((addr>= p->addr&& (addr< p->addr + p->length)));
    >>> +}
    >>>
    >>
    >> I think I see a problem here. For virtio, we do not necessarily want all
    >> virtqueues for a device to live in kernel: there might be control
    >> virtqueues that we want to leave in userspace. Since this claims all
    >> writes to a specific address, the signal never makes it to userspace.
    >>
    >
    > Userspace could create an eventfd for this control queue and wait for it
    > to fire.

    What if guest writes an unexpected value there?
    The value it simply lost ... that's not very elegant.

    --
    MST


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