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

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Message-ID: <20071112133207.GJ3299@rhun.haifa.ibm.com>
Date:	Mon, 12 Nov 2007 15:32:07 +0200
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	Amit Shah <amit.shah@...ranet.com>
Cc:	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 05:26:24PM +0530, Amit Shah wrote:
> On Monday 12 November 2007 16:20:01 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...).
> 
> That would make great sense and simplify implementations.
> 
> How do you propose such an implementation? An array of function
> pointers for each possible call?

I was thinking of simply a chain of dma_ops (via dma_ops->prev_ops) ,
where it's the responsibility of each dma_ops implementation to call
or not call the corresponding entry in chain (prev_ops->op()). This
works well for Calgary (which will only use prev_ops selectively, and
I think it will work well for the IB folks. Will it work for you?

Cheers,
Muli
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