linux-kernel - Re: [PATCH v2 2/2] iommu/arm-smmu-v3: Configure STU of a PF if ATS is not enabled.

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Date:   Mon, 13 Mar 2023 19:49:20 +0530
From:   Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
To:     linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev,
        joro@...tes.org, bhelgaas@...gle.com, robin.murphy@....com,
        will@...nel.org
Cc:     jean-philippe@...aro.org,
        sathyanarayanan.kuppuswamy@...ux.intel.com,
        darren@...amperecomputing.com, scott@...amperecomputing.com
Subject: Re: [PATCH v2 2/2] iommu/arm-smmu-v3: Configure STU of a PF if ATS is
 not enabled.


Hi Will, Robin,

On 28-02-2023 09:51 am, Ganapatrao Kulkarni wrote:
> When the host kernel is booted with iommu passthrough mode, PF and VFs
> are enumerated with iommu/smmu domain set to bypass mode.
> In bypass mode, ATS is not enabled on all VFs and associated PF.
> When VFs are attached to a VM, the corresponding iommu domain is set to
> SMMU translation mode and smmu-v3 driver try to enable the ATS and fails
> due to invalid STU of a PF.
> 
> Adding a fix to configure STU of a PF while enumerating in passthrough
> mode.
> 

Any comments on this patch/series?

> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 25 ++++++++++++++++++++-
>   1 file changed, 24 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index f2425b0f0cd6..b218ef0bf001 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2292,6 +2292,23 @@ static bool arm_smmu_ats_supported(struct arm_smmu_master *master)
>   	return dev_is_pci(dev) && pci_ats_supported(to_pci_dev(dev));
>   }
>   
> +static void arm_smmu_ats_stu_init(struct arm_smmu_master *master)
> +{
> +	size_t stu;
> +	struct pci_dev *pdev;
> +	struct arm_smmu_device *smmu = master->smmu;
> +
> +	if (master->ats_enabled)
> +		return;
> +
> +	/* Smallest Translation Unit: log2 of the smallest supported granule */
> +	stu = __ffs(smmu->pgsize_bitmap);
> +	pdev = to_pci_dev(master->dev);
> +
> +	if (pci_ats_stu_configure(pdev, stu))
> +		dev_err(master->dev, "Failed to configure ATS STU (%zu)\n", stu);
> +}
> +
>   static void arm_smmu_enable_ats(struct arm_smmu_master *master)
>   {
>   	size_t stu;
> @@ -2404,6 +2421,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   	struct arm_smmu_device *smmu;
>   	struct arm_smmu_domain *smmu_domain = to_smmu_domain(domain);
>   	struct arm_smmu_master *master;
> +	bool ats_supported;
>   
>   	if (!fwspec)
>   		return -ENOENT;
> @@ -2446,9 +2464,10 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   	}
>   
>   	master->domain = smmu_domain;
> +	ats_supported = arm_smmu_ats_supported(master);
>   
>   	if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
> -		master->ats_enabled = arm_smmu_ats_supported(master);
> +		master->ats_enabled = ats_supported;
>   
>   	arm_smmu_install_ste_for_dev(master);
>   
> @@ -2458,6 +2477,10 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   
>   	arm_smmu_enable_ats(master);
>   
> +	/* Configure ATS STU of a PF in passthrough */
> +	if (!master->ats_enabled && ats_supported)
> +		arm_smmu_ats_stu_init(master);
> +
>   out_unlock:
>   	mutex_unlock(&smmu_domain->init_mutex);
>   	return ret;

Thanks,
Ganapat