linux-kernel - Re: [PATCHv9 3/8] iommu/arm-smmu: Move non-strict mode to use io_pgtable_domain

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Message-ID: <d4c7f311fbea91bb63d3b0eb164cf0d3@codeaurora.org>
Date:   Wed, 25 Nov 2020 11:06:02 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Will Deacon <will@...nel.org>
Cc:     Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Jordan Crouse <jcrouse@...eaurora.org>,
        Rob Clark <robdclark@...il.com>,
        Akhil P Oommen <akhilpo@...eaurora.org>,
        freedreno@...ts.freedesktop.org,
        "Kristian H . Kristensen" <hoegsberg@...gle.com>,
        dri-devel@...ts.freedesktop.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCHv9 3/8] iommu/arm-smmu: Move non-strict mode to use
 io_pgtable_domain_attr

On 2020-11-25 03:09, Will Deacon wrote:
> On Mon, Nov 23, 2020 at 10:35:56PM +0530, Sai Prakash Ranjan wrote:
>> Now that we have a struct io_pgtable_domain_attr with quirks,
>> use that for non_strict mode as well thereby removing the need
>> for more members of arm_smmu_domain in the future.
>> 
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> ---
>>  drivers/iommu/arm/arm-smmu/arm-smmu.c | 8 +++-----
>>  drivers/iommu/arm/arm-smmu/arm-smmu.h | 1 -
>>  2 files changed, 3 insertions(+), 6 deletions(-)
>> 
>> diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c 
>> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> index 4b9b10fe50ed..f56f266ebdf7 100644
>> --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
>> @@ -786,9 +786,6 @@ static int arm_smmu_init_domain_context(struct 
>> iommu_domain *domain,
>>  			goto out_clear_smmu;
>>  	}
>> 
>> -	if (smmu_domain->non_strict)
>> -		pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
>> -
>>  	if (smmu_domain->pgtbl_cfg.quirks)
>>  		pgtbl_cfg.quirks |= smmu_domain->pgtbl_cfg.quirks;
>> 
>> @@ -1527,7 +1524,8 @@ static int arm_smmu_domain_get_attr(struct 
>> iommu_domain *domain,
>>  	case IOMMU_DOMAIN_DMA:
>>  		switch (attr) {
>>  		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
>> -			*(int *)data = smmu_domain->non_strict;
>> +			if (smmu_domain->pgtbl_cfg.quirks & IO_PGTABLE_QUIRK_NON_STRICT)
>> +				*(int *)data = smmu_domain->pgtbl_cfg.quirks;
> 
> I still don't think this is right :(
> We need to set *data to 1 or 0 depending on whether or not the 
> non-strict
> quirk is set, i.e:
> 
> 	bool non_strict = smmu_domain->pgtbl_cfg.quirks & 
> IO_PGTABLE_QUIRK_NON_STRICT;
> 	*(int *)data = non_strict;
> 
> Your code above leaves *data uninitialised if non_strict is not set.

Ugh sorry, I should have looked at this some more before hurrying up
to post, will fix it.

> 
>>  			return 0;
>>  		default:
>>  			return -ENODEV;
>> @@ -1578,7 +1576,7 @@ static int arm_smmu_domain_set_attr(struct 
>> iommu_domain *domain,
>>  	case IOMMU_DOMAIN_DMA:
>>  		switch (attr) {
>>  		case DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE:
>> -			smmu_domain->non_strict = *(int *)data;
>> +			smmu_domain->pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_NON_STRICT;
> 
> And this is broken because if *data is 0, then you _set_ the quirk, 
> which is
> the opposite of what we should be doing.
> 
> In other words, although the implementation has changed, the semantics 
> have
> not.
> 

Will fix this to have quirk set only when *data = 1 and unset in case of 
0.

Thanks,
Sai

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