Re: [PATCH 2/4] iommu/arm-smmu-v3: Rework enabling/disabling of ATS for PCI masters

[Robin Murphy <robin.murphy@arm.com>]

On 20/08/2019 16:45, Will Deacon wrote:
> To prevent any potential issues arising from speculative Address
> Translation Requests from an ATS-enabled PCIe endpoint, rework our ATS
> enabling/disabling logic so that we enable ATS at the SMMU before we
> enable it at the endpoint, and disable things in the opposite order.
> 
> Signed-off-by: Will Deacon <will@kernel.org>
> ---
>   drivers/iommu/arm-smmu-v3.c | 44 ++++++++++++++++++++++++++------------------
>   1 file changed, 26 insertions(+), 18 deletions(-)
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 3402b1bc8e94..9096eca0c480 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2283,31 +2283,34 @@ static void arm_smmu_install_ste_for_dev(struct arm_smmu_master *master)
>   	}
>   }
>   
> -static int arm_smmu_enable_ats(struct arm_smmu_master *master)
> +static bool arm_smmu_ats_supported(struct arm_smmu_master *master)
>   {
> -	int ret;
> -	size_t stu;
>   	struct pci_dev *pdev;
>   	struct arm_smmu_device *smmu = master->smmu;
>   	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(master->dev);
>   
>   	if (!(smmu->features & ARM_SMMU_FEAT_ATS) || !dev_is_pci(master->dev) ||
>   	    !(fwspec->flags & IOMMU_FWSPEC_PCI_RC_ATS) || pci_ats_disabled())
> -		return -ENXIO;
> +		return false;
>   
>   	pdev = to_pci_dev(master->dev);
> -	if (pdev->untrusted)
> -		return -EPERM;
> +	return !pdev->untrusted && pdev->ats_cap;
> +}
>   
> -	/* Smallest Translation Unit: log2 of the smallest supported granule */
> -	stu = __ffs(smmu->pgsize_bitmap);
> +static void arm_smmu_enable_ats(struct arm_smmu_master *master)
> +{
> +	size_t stu;
> +	struct pci_dev *pdev;
> +	struct arm_smmu_device *smmu = master->smmu;
>   
> -	ret = pci_enable_ats(pdev, stu);
> -	if (ret)
> -		return ret;
> +	if (master->ats_enabled || !dev_is_pci(master->dev))
> +		return;
>   
> -	master->ats_enabled = true;
> -	return 0;
> +	/* Smallest Translation Unit: log2 of the smallest supported granule */
> +	stu = __ffs(smmu->pgsize_bitmap);
> +	pdev = to_pci_dev(master->dev);
> +	if (pci_enable_ats(pdev, stu))
> +		dev_err(master->dev, "Failed to enable ATS (STU %zu)\n", stu);
>   }
>   
>   static void arm_smmu_disable_ats(struct arm_smmu_master *master)
> @@ -2317,10 +2320,14 @@ static void arm_smmu_disable_ats(struct arm_smmu_master *master)
>   	if (!master->ats_enabled || !dev_is_pci(master->dev))

Hmm, while you've got the lid off, that dev_is_pci() test is clearly 
redundant.

>   		return;
>   
> +	pci_disable_ats(to_pci_dev(master->dev));
> +	/*
> +	 * Ensure ATS is disabled at the endpoint before we issue the
> +	 * ATC invalidation via the SMMU.
> +	 */
> +	wmb();
>   	arm_smmu_atc_inv_to_cmd(0, 0, 0, &cmd);
>   	arm_smmu_atc_inv_master(master, &cmd);
> -	pci_disable_ats(to_pci_dev(master->dev));
> -	master->ats_enabled = false;
>   }
>   
>   static void arm_smmu_detach_dev(struct arm_smmu_master *master)
> @@ -2335,10 +2342,10 @@ static void arm_smmu_detach_dev(struct arm_smmu_master *master)
>   	list_del(&master->domain_head);
>   	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
>   
> +	arm_smmu_disable_ats(master);
>   	master->domain = NULL;
> +	master->ats_enabled = false;
>   	arm_smmu_install_ste_for_dev(master);
> -
> -	arm_smmu_disable_ats(master);
>   }
>   
>   static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
> @@ -2383,12 +2390,13 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   	spin_unlock_irqrestore(&smmu_domain->devices_lock, flags);
>   
>   	if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
> -		arm_smmu_enable_ats(master);
> +		master->ats_enabled = arm_smmu_ats_supported(master);

So for non-bypass domains we pretend ATS is already enabled iff it could 
possibly be...

>   	if (smmu_domain->stage == ARM_SMMU_DOMAIN_S1)
>   		arm_smmu_write_ctx_desc(smmu, &smmu_domain->s1_cfg);
>   
>   	arm_smmu_install_ste_for_dev(master);
> +	arm_smmu_enable_ats(master);

...which ensures this won't actually touch the PCIe cap, unless of 
course when STE.EATS == 0. Are you sure about that?

Robin.

>   out_unlock:
>   	mutex_unlock(&smmu_domain->init_mutex);
>   	return ret;
> 
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