Verify if XShmPutImage() works fine when VT-d is enabled

[marmarek]

Reported by joanna on 20 Apr 2010 22:06 UTC
According to this message:
http://groups.google.com/group/qubes-devel/msg/9d23cd9c26127ed7

The XShmPutImage() function, that is used by guid in Dom0 to draw the actual app's pixmap, might attempt to schedule a DMA from the SHM region to video memory. The SHM memory in our case belongs originaly to DomU and is being brought to Dom0 via xc_map_foreign_pages() (see http://qubes-os.org/gitweb/?p=rafal/gui.git;a=blob;f=shmoverride/shmoverride.c;h=77be2127948436013dc8a57ea069901a5d33ec03;hb=HEAD#l48).

If xc_map_foreign_pages() doesn't update IOMMU/VT-d tables so that the mapped pages belong also to Dom0, than the graphics card, that is VT-d assigned to Dom0, would not be able to do DMA read from those pages, and so the XShmPutImage() might not work correctly (not at all in fact).

TODO: check if xc_map_foreign_pages() updates IOMMU/VT-d tables, and if not discuss a way to add such behaviour on xen-devel and implement a patch.

Migrated-From: https://wiki.qubes-os.org/ticket/23

[marmarek]

Comment by joanna on 13 May 2010 12:39 UTC
No need to worry! All should work fine -- see this thread:

http://lists.xensource.com/archives/html/xen-devel/2010-05/msg00667.html

[marmarek]

Comment by joanna on 13 May 2010 12:39 UTC
No need to worry! All should work fine -- see this thread:

http://lists.xensource.com/archives/html/xen-devel/2010-05/msg00667.html

[marmarek]

Modified by joanna on 27 Jul 2010 14:58 UTC

[marmarek]

Modified by joanna on 27 Jul 2010 14:58 UTC