Re: [Xen-devel] [PATCH v2 3/5] tools/libxendevicemodel: extract functions and add a compat layer

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

Paul Durrant writes ("[PATCH v2 3/5] tools/libxendevicemodel: extract functions 
and add a compat layer"):
> This patch extracts all functions resulting in a dm_op hypercall from
> libxenctrl and moves them into libxendevicemodel. It also adds a compat
> layer into libxenctrl, which can be selected by defining
> XC_WANT_COMPAT_DEVICEMODEL_API to 1 before including xenctrl.h.
> 
> With this patch the core of libxendevicemodel still uses libxencall to
> issue the dm_op hypercalls, but this is done by calling through code that
> can be modified on a per-OS basis. A subsequent patch will add a Linux-
> specific variant.
...
> +int xendevicemodel_track_dirty_vram(
> +    xendevicemodel_handle *dmod, domid_t domid, uint64_t first_pfn,
> +    uint32_t nr, unsigned long *dirty_bitmap)
> +{
> +    struct xen_dm_op op;
> +    struct xen_dm_op_track_dirty_vram *data;
> +
> +    memset(&op, 0, sizeof(op));
> +
> +    op.op = XEN_DMOP_track_dirty_vram;
> +    data = &op.u.track_dirty_vram;
> +
> +    data->first_pfn = first_pfn;
> +    data->nr = nr;
> +
> +    return xendevicemodel_op(dmod, domid, 2, &op, sizeof(op),
> +                             dirty_bitmap, (size_t)(nr + 7) / 8);
> +}

As I think we discussed some time last week (?), this function cannot
be a DMOP.  This is because enabling track_dirty_vram causes the
hypervisor to remember the memory referred to by dirty_bitmap, but the
dmop privcmd restriction mechanism only guarantees that the memory is
valid and belonging to this guest _during the hypercall_.

Are there more like this ?  How does ioreq server registration
work ?

Can we add a note to the hypervisor side of the DMOP buffer interface,
saying something like

   Code in Xen MUST NOT save copies of the pointers in the dmop
   buffers.  Only copying to and from guest memory, during the
   hypercall, is permitted.

?

Ian.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
https://lists.xen.org/xen-devel