Re: [PATCH 2 of 5] add can_dma/post_dma for direct IO

Gerd Hoffmann
2008-12-12T20:26:15Z

Andrea Arcangeli wrote:
> On Fri, Dec 12, 2008 at 01:15:13PM -0600, Anthony Liguori wrote:
>> 1) You attempt to map a physical address. This effectively is a lock or
>> pin operation.
>
> lock or pin for what? There's nothing to pin or lock here.

Oh, there is in Xen context (i.e. qemu in dom0 handles device emulation
for xen domU guests). You can ask Xen to map the grant (or guest pfn)
here. I think doing so will kill the need for the mapcache patches
xensource carries in the xenified qemu tree.

>> 4) You unmap or unlock that memory region. The virtual address is now no
>> longer valid.
>
> Again not needed.

Likewise useful for Xen.

cheers,
Gerd