linux-kernel - Re: [PATCH 2/6] iommu/qcom: Write TCR before TTBRs to fix ASID access behavior

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Date:   Tue, 31 May 2022 16:55:59 +0100
From:   Will Deacon <will@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        linux-arm-msm@...r.kernel.org, bjorn.andersson@...aro.org,
        linux-arm-kernel@...ts.infradead.org,
        iommu@...ts.linux-foundation.org, martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, jamipkettunen@...ainline.org,
        Rob Clark <robdclark@...il.com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/6] iommu/qcom: Write TCR before TTBRs to fix ASID
 access behavior

On Fri, May 27, 2022 at 11:28:57PM +0200, Konrad Dybcio wrote:
> From: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> 
> As also stated in the arm-smmu driver, we must write the TCR before
> writing the TTBRs, since the TCR determines the access behavior of
> some fields.

Where is this stated in the arm-smmu driver?

> 
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...ainline.org>
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...ainline.org>
> ---
>  drivers/iommu/arm/arm-smmu/qcom_iommu.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu/qcom_iommu.c b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> index 1728d4d7fe25..75f353866c40 100644
> --- a/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> +++ b/drivers/iommu/arm/arm-smmu/qcom_iommu.c
> @@ -273,18 +273,18 @@ static int qcom_iommu_init_domain(struct iommu_domain *domain,
>  			ctx->secure_init = true;
>  		}
>  
> -		/* TTBRs */
> -		iommu_writeq(ctx, ARM_SMMU_CB_TTBR0,
> -				pgtbl_cfg.arm_lpae_s1_cfg.ttbr |
> -				FIELD_PREP(ARM_SMMU_TTBRn_ASID, ctx->asid));
> -		iommu_writeq(ctx, ARM_SMMU_CB_TTBR1, 0);
> -
>  		/* TCR */
>  		iommu_writel(ctx, ARM_SMMU_CB_TCR2,
>  				arm_smmu_lpae_tcr2(&pgtbl_cfg));
>  		iommu_writel(ctx, ARM_SMMU_CB_TCR,
>  			     arm_smmu_lpae_tcr(&pgtbl_cfg) | ARM_SMMU_TCR_EAE);
>  
> +		/* TTBRs */
> +		iommu_writeq(ctx, ARM_SMMU_CB_TTBR0,
> +				pgtbl_cfg.arm_lpae_s1_cfg.ttbr |
> +				FIELD_PREP(ARM_SMMU_TTBRn_ASID, ctx->asid));
> +		iommu_writeq(ctx, ARM_SMMU_CB_TTBR1, 0);

I'd have thought that SCTLR.M would be clear here, so it shouldn't matter
what order we write these in.

Will