linux-kernel - Re: [PATCH 2/2] ARM: SMMU: return NULL on error in arm_smmu_iova_to

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Date:	Thu, 7 Nov 2013 18:58:06 +0000
From:	Will Deacon <will.deacon@....com>
To:	Antonios Motakis <a.motakis@...tualopensystems.com>
Cc:	Joerg Roedel <joro@...tes.org>,
	"moderated list:ARM SMMU DRIVER" 
	<linux-arm-kernel@...ts.infradead.org>,
	"open list:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
	open list <linux-kernel@...r.kernel.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	"tech@...tualopensystems.com" <tech@...tualopensystems.com>,
	"agraf@...e.de" <agraf@...e.de>,
	"B08248@...escale.com" <B08248@...escale.com>
Subject: Re: [PATCH 2/2] ARM: SMMU: return NULL on error in
 arm_smmu_iova_to_phys

On Mon, Oct 14, 2013 at 06:09:48PM +0100, Will Deacon wrote:
> On Mon, Oct 14, 2013 at 04:17:51PM +0100, Antonios Motakis wrote:
> > On Mon, Oct 14, 2013 at 2:48 PM, Will Deacon <will.deacon@....com> wrote:
> > > On Fri, Oct 11, 2013 at 02:24:47PM +0100, Antonios Motakis wrote:
> > VFIO will exercise this code path every time when mapping DMA memory.
> > This is normal and VFIO *expects* the function to fail - it is only if
> > the function succeeds that VFIO needs to back down from the DMA
> > mapping and fail.
> > 
> > This means that there would be a warning every time a VFIO user maps
> > some memory for DMA use, even though nothing went wrong.
> 
> Ok, in which case it might be worth reworking arm_smmu_iova_to_phys to treat
> {pgd,pud,pmd,pte}_none different from {pgd,pud,pmd,pte}_bad.

Just an FYI, but I realised the page table locking is broken in my driver
(hold a spinlock over a non-atomic allocation; looks like the exynos guys do
this too), so I've just reworked a bunch of iova_to_phys and incorporated this
change as part of that.

Cheers,

Will
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