linux-kernel - Re: [kvm-devel] [PATCH 3/8] KVM: PVDMA Guest: Guest-side routines for paravirtualized DMA

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Message-ID: <20071112160023.GG6466@amd.com>
Date:	Mon, 12 Nov 2007 17:00:23 +0100
From:	"Joerg Roedel" <joerg.roedel@....com>
To:	"Muli Ben-Yehuda" <muli@...ibm.com>
cc:	"Amit Shah" <amit.shah@...ranet.com>,
	kvm-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [kvm-devel] [PATCH 3/8] KVM: PVDMA Guest: Guest-side
 routines for paravirtualized DMA

On Mon, Nov 12, 2007 at 12:50:01PM +0200, Muli Ben-Yehuda wrote:
> On Wed, Nov 07, 2007 at 04:21:04PM +0200, Amit Shah wrote:
> 
> > We make the dma_mapping_ops structure to point to our structure so
> > that every DMA access goes through us. (This is the reason this only
> > works for 64-bit guest. 32-bit guest doesn't yet have a dma_ops
> > struct.)
> 
> I need the same facility for Calgary for falling back to swiotlb if a
> translation is disabled on some slot, and IB needs the same facility
> for some IB adapters (e.g., ipath). Perhaps it's time to consider
> stackable dma-ops (unless someone has a better idea...).

Stackable dma-ops sounds good to me. The only problem is that there is a
performance penalty for devices handled on the bottom of the stack. But
the alternative I can think of, a per-device dma-ops structure, uses more
memory and is much more intrusive to the driver core. So I am fine with
a stackable solution.

Joerg

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