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

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Date:   Tue, 24 Nov 2020 21:39:18 +0000
From:   Will Deacon <will@...nel.org>
To:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.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 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.

>  			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