linux-kernel - Re: [Alacrityvm-devel] [PATCH v2 2/4] KVM: introduce "xinterface" API for external interaction with guests

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Message-ID: <4ACC46A2.2090103@redhat.com>
Date:	Wed, 07 Oct 2009 09:43:30 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Ira W. Snyder" <iws@...o.caltech.edu>
CC:	Gregory Haskins <gregory.haskins@...il.com>,
	David Howells <dhowells@...hat.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	"alacrityvm-devel@...ts.sourceforge.net" 
	<alacrityvm-devel@...ts.sourceforge.net>
Subject: Re: [Alacrityvm-devel] [PATCH v2 2/4] KVM: introduce "xinterface"
 API for external	interaction with guests

On 10/06/2009 08:18 PM, Ira W. Snyder wrote:
>
> The limitation I have is that memory made available from the host system
> (PCI card) as PCI BAR1 must not be migrated around in memory. I can only
> change the address decoding to hit a specific physical address. AFAIK,
> this means it cannot be userspace memory (since the underlying physical
> page could change, or it could be in swap), and must be allocated with
> something like __get_free_pages() or dma_alloc_coherent().
>    

Expose it as /dev/something (/dev/mem, /sys/.../pci/...) and mmap() it, 
and it becomes non-pageable user memory.

Not sure about dma_alloc_coherent(), that is meaningless on x86.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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