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

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Message-ID: <CAG8rG2yE=xWmYP_bOy7=jzWEQKNkbgk-9_Jecnx_XXx=jC9i_Q@mail.gmail.com>
Date:	Mon, 14 Oct 2013 17:17:51 +0200
From:	Antonios Motakis <a.motakis@...tualopensystems.com>
To:	Will Deacon <will.deacon@....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 2:48 PM, Will Deacon <will.deacon@....com> wrote:
> On Fri, Oct 11, 2013 at 02:24:47PM +0100, Antonios Motakis wrote:
>> The return value of arm_smmu_iova_to_phys is directly passed to the
>> user of the IOMMU API via iommu_iova_to_phys; however the ARM SMMU
>> driver returns -EINVAL on error, which is not consistent with the
>> rest of the drivers implementing the IOMMU API. VFIO also relies on
>> the call returning NULL when a page has not been mapped already.
>>
>> Signed-off-by: Antonios Motakis <a.motakis@...tualopensystems.com>
>> ---
>>  drivers/iommu/arm-smmu.c | 5 +----
>>  1 file changed, 1 insertion(+), 4 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
>> index 8b71332..fe81b20 100644
>> --- a/drivers/iommu/arm-smmu.c
>> +++ b/drivers/iommu/arm-smmu.c
>> @@ -1480,10 +1480,7 @@ static phys_addr_t arm_smmu_iova_to_phys(struct iommu_domain *domain,
>>
>>  err_unlock:
>>       spin_unlock(&smmu_domain->lock);
>> -     dev_warn(smmu->dev,
>> -              "invalid (corrupt?) page tables detected for iova 0x%llx\n",
>> -              (unsigned long long)iova);
>> -     return -EINVAL;
>> +     return NULL;
>
> Why are you removing the warning message?

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.

>
> Will
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