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Re: [Xen-devel] Assigning contiguous memory to a driver domain

On Mon, Sep 20, 2010 at 01:27:24PM -0700, Jeremy Fitzhardinge wrote:
>  On 09/20/2010 12:48 PM, Konrad Rzeszutek Wilk wrote:
> > Let me expand this. During bootup Xen-SWIOTLB  (which for DomU you have
> > to enable via the 'iommu=soft'), allocated 32 2MB chunks of contingous
> > memory under the 4GB limit. Those chunks stay in DomU and are used
> > during the the runtime of the DomU. They don't go back to Xen unless the
> > domain has been terminated. Any of the DMA operations that any driver
> > does go through the SWIOTLB bufer if the physical (mfn) for the DMA is
> > outside the driver capabilities (say, your ping buffer is allocated above
> > the 4GB, and your r8169 can only do 32-bit, then SWIOTLB would be utilized
> > to "bounce" the memory).
> BTW, are there any hooks to make sure these pages are still contiguous
> after migration/restore?

<shudders>I don't really know. We do save the P2M map, so those mappings
are saved in the guest. But for the MFNs that have been exchanged - I don't
believe the hypervior is notified about which MFNs have been transfered
to another domain? Or these MFNs extracted during save/resume?

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