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RE: [Xen-devel] swiotlb and Xen query?

  • To: "pradeep singh rautela" <rautelap@xxxxxxxxx>
  • From: "Petersson, Mats" <Mats.Petersson@xxxxxxx>
  • Date: Thu, 3 May 2007 11:19:10 +0200
  • Cc: xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
  • Delivery-date: Thu, 03 May 2007 02:18:19 -0700
  • List-id: Xen developer discussion <xen-devel.lists.xensource.com>
  • Thread-index: AceNPVbMSVqCCG7GSZWvraYZz+4eugAJoWDQ
  • Thread-topic: [Xen-devel] swiotlb and Xen query?

> That was really very informative Mats.
> Thanks you very much for the help.
> So, i guess swiotlb comes into picture only if there is a DMA 
> transfer from a domU whose p2m mapping turns out to be above 
> the 4GB( assuming device to be 32 bit) of the machine memory. 
> Other wise just normal p2m mapping is enough to find the 
> actual machine address, which can be handed over to the 
> device for DMAing. Am i right? 

Yes, that's pretty much how it works. In theory, it could be that
devices only work on a 31, 28 or some other number of bit-range, but
yes, that's the principle. 

> Thank you once again for the patience. 
> Regards
> ~psr

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