linux-kernel - Re: [PATCH v2 -mm 0/2] x86: per-device dma_mapping

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Message-ID: <20080525072011.GM7334@il.ibm.com>
Date:	Sun, 25 May 2008 10:20:11 +0300
From:	Muli Ben-Yehuda <muli@...ibm.com>
To:	Amit Shah <amit.shah@...ranet.com>
Cc:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	alexisb@...ibm.com, andi@...stfloor.org, kvm@...r.kernel.org,
	avi@...ranet.com
Subject: Re: [PATCH v2 -mm 0/2] x86: per-device dma_mapping_ops

On Thu, May 22, 2008 at 04:13:02PM +0530, Amit Shah wrote:

> OK; this sounds helpful. the hook can make a hypercall and confirm
> with the host kernel if the device in question is an assigned
> physical device. If yes, we replace the dma_ops. Though, the
> original intent of having stackable ops is that we might want to go
> through the swiotlb in the guest even for an assigned device if the
> guest dma addresses are not in the addressable range of the guest
> chipset.
> 
> > created (it works with hot plugging). It enables IOMMUs to set up an
> > appropriate dma_mapping_ops per device.
> 
> From what we've discussed so far, it looks like stackable dma ops will 
> definitely be needed. Does this patchset provide something that stacking 
> won't?

Yes---this patchset let's you have a per-device dma-ops, whereas with
stackable you only get global dma-ops. I think it's clear we need
both, and I think per-device dma-ops are the first thing that's
needed. Stacking can then be introduced on a per-device basis.

Cheers,
Muli

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