linux-kernel - Re: [PATCH linux-next] iommu: add iommu for s390 platform

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Message-ID: <20141023124115.GB10053@8bytes.org>
Date:	Thu, 23 Oct 2014 14:41:15 +0200
From:	Joerg Roedel <joro@...tes.org>
To:	Frank Blaschka <blaschka@...ux.vnet.ibm.com>
Cc:	schwidefsky@...ibm.com, linux-kernel@...r.kernel.org,
	linux-s390@...r.kernel.org, iommu@...ts.linux-foundation.org,
	sebott@...ux.vnet.ibm.com, gerald.schaefer@...ibm.com
Subject: Re: [PATCH linux-next] iommu: add iommu for s390 platform

On Wed, Oct 22, 2014 at 05:43:20PM +0200, Frank Blaschka wrote:
> Basically there are no limitations. Depending on the s390 maschine
> generation a device starts its IOVA at a specific address (announced by
> the HW). But as I already told each device starts at the same address.
> I think this prevents having multiple devices on the same IOMMU domain.

Why, each device has its own IOVA address space, so IOVA A could map to
physical address X for one device and to Y for another, no? And if you
point multiple devices to the same dma_table they share the mappings
(and thus the address space). Or am I getting something wrong?

> yes, you are absolutely right. There is a per-device dma_table.
> There is no general IOMMU device but each pci device has its own IOMMU
> translation capability.

I see, in this way it is similar to ARM where there is often also one IOMMU
per master device.

> Is there a possibility the IOMMU domain can support e.g. something like
> 
> VIOA 0x10000 -> pci device 1
> VIOA 0x10000 -> pci device 2

A domain is basically an abstraction for a DMA page table (or a
dma_table, as you call it on s390). So you can easily create similar
mappings for more than one device with it.



	Joerg

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