linux-kernel - Re: BUG: SCSI aic7xxx driver and AMD IOMMU

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Message-ID: <20150326155248.GW4441@8bytes.org>
Date:	Thu, 26 Mar 2015 16:52:49 +0100
From:	Joerg Roedel <joro@...tes.org>
To:	Mark Hounschell <markh@...pro.net>
Cc:	iommu@...ts.linux-foundation.org, Hannes Reinecke <hare@...e.de>,
	"linux-scsi@...r.kernel.org >> SCSI development list" 
	<linux-scsi@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: BUG: SCSI aic7xxx driver and AMD IOMMU

Hi Mark,

On Thu, Mar 26, 2015 at 10:58:15AM -0400, Mark Hounschell wrote:
> Sorry but CMA was still badly broken. I have a patch below that works.

In which way is it broken? What happens when you try to allocate memory
with dma_alloc_coherent?

> I've tested it with small (no CMA) and large (with CMA) dma's using
> dma_alloc_coherent. The patch below is just the "git diff" from your
> cloned tree piped to a file then copied into this email. If you require
> an official patch I can send one. Just let me know.

The main differences I can spot are that you change the order (first
CMA, then buddy) and you manually align the input size. I can see the
reason for the later, but why does CMA need to be tried first?

> Also, in my opinion, this CMA thing is clearly a BUG not a feature
> request. The AMD iommu clearly breaks CMA. I feel what ever fix
> you are happy with should be back ported to stable.

It is not a BUG, the interface definition for dma_alloc_coherent does
not specify that it can allocate infinite amounts of memory. So this
patch does not qualify for stable.


	Joerg

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