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Re: [Xen-users] Question on pseudo-physical memory

from [Muli Ben-Yehuda]

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To:	mjfeeney@xxxxxxxxxxx
Subject:	Re: [Xen-users] Question on pseudo-physical memory
From:	Muli Ben-Yehuda <muli@xxxxxxxxxx>
Date:	Wed, 2 Aug 2006 08:43:06 +0300
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On Tue, Aug 01, 2006 at 01:04:22PM -0400, mjfeeney@xxxxxxxxxxx wrote:

> Does this mean that a Domain0 Linux kernel driver which allocated
> kernel memory with kmalloc() or __get_free_pages() may not receive
> memory that is physically contiguous in the underlying real memory?

Yep.

> I ask because this could cause an issue for a device driver that
> must build scatter/gather lists for an external device.  If this is
> true, is there documentation available on what's required to build a
> valid scatter/gather list which contains real physically contiguous
> segments?

If your driver is using the DMA API properly as it should, this should
"just work", since the XenLinux DMA API implementations do the right
thing (e.g., using swiotlb for bouncing buffer which are not contigous
in machine memory).

Cheers,
Muli



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