RE: [Xen-devel] [PATCH 0/5] VT-d support for PV guests

[Espen Skoglund <espen.skoglund@xxxxxxxxxxxxx>]

[Xiaowei Yang]
> Espen,
> The patches look good to me with some comments:

> - For the occasions when P2M is changed, the hooks of
> iommu_{un}map_page() can be added cleaner. Only the hooks inside
> guest_physmap_add/remove_page() are necessary. The hooks in
> populate_physmap() and memory_exchange() can be omitted by some
> small code rearrangement like removing if(paging_mode_translate(d))
> before calling guest_physmap_add_page().

Yes.  I considered this as an option as well, but ended up with the
current approach.  Your suggestion is probably cleaner, so I'll switch
over to doing that.


> - gnttab_map/unmap_grant_ref() need to be hooked also. There are no
> P2M changes at that time while the guest PT is updated directly. The
> mapped pages can also be used for DMA by backend drivers.

Thanks.  Overlooked that one.  Only caught the gnttab_transfer().


> - dom0 can be treated as the same as other PV domains with regard to
> VTd PT updating. Unfortunately, it need some special care. All of
> devices are assigned to it by default and usually it ones the most
> of devices.  iommu_{un}map_page() could be called very frequently by
> it while it serves other domains IO requests. It will bring
> performance penalty and CPU overhead.

dom0 should not need to do any VT-d page table updating once it has
been set up, so marking it as need_iommu() should be unnecessary.
Also, if passthrough mode is supported in VT-d then dom0 does not need
to have VT-d page tables at all.  I think setting it's VT-d tables up
to have complete access at startup and leave it that way is perfectly
fine.


Thanks for feedback.  Will repost once I've incorporated all the
comments.

        eSk




_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel