Date: Mon, 12 Nov 2007 15:32:07 +0200
From: Muli Ben-Yehuda <muli@il.ibm.com>
To: Amit Shah <amit.shah@qumranet.com>
Cc: kvm-devel@lists.sourceforge.net, linux-kernel@vger.kernel.org
Subject: Re: [kvm-devel] [PATCH 3/8] KVM: PVDMA Guest: Guest-side routines for paravirtualized DMA
Message-ID: <20071112133207.GJ3299@rhun.haifa.ibm.com>
References: <d1c72ce6e3a0e73c18993c3f066d1350b147f726.1194445109.git.amit.shah@qumranet.com> <609d5d611a5fb58ab5a7184be7b6d29494023ba0.1194445109.git.amit.shah@qumranet.com> <20071112105001.GF3299@rhun.haifa.ibm.com> <200711121726.24907.amit.shah@qumranet.com>
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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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