linux-kernel - Re: [PATCH] iommu/arm-smmu-v3: Enable PCI ATS in passthrough mode as well

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Date:   Thu, 2 Feb 2023 13:22:07 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        iommu@...ts.linux.dev, will@...nel.org, joro@...tes.org
Cc:     jean-philippe@...aro.org, darren@...amperecomputing.com,
        scott@...amperecomputing.com
Subject: Re: [PATCH] iommu/arm-smmu-v3: Enable PCI ATS in passthrough mode as
 well

On 2023-02-02 12:40, Ganapatrao Kulkarni wrote:
> The current smmu-v3 driver does not enable PCI ATS for physical functions
> of ATS capable End Points when booted in smmu bypass mode
> (iommu.passthrough=1). This will not allow virtual functions to enable
> ATS(even though EP supports it) while they are attached to a VM using
> VFIO driver.
> 
> This patch adds changes to enable ATS support for physical functions
> in passthrough/bypass mode as well.
> 
> Also, adding check to avoid disabling of ATS if it is not enabled,
> to avoid unnecessary call-traces.
> 
> Signed-off-by: Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>
> ---
>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> 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 6d5df91c5c46..5a605cb5ccef 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -2313,11 +2313,16 @@ static void arm_smmu_enable_ats(struct arm_smmu_master *master)
>   static void arm_smmu_disable_ats(struct arm_smmu_master *master)
>   {
>   	struct arm_smmu_domain *smmu_domain = master->domain;
> +	struct pci_dev *pdev;
>   
>   	if (!master->ats_enabled)
>   		return;
>   
> -	pci_disable_ats(to_pci_dev(master->dev));
> +	pdev = to_pci_dev(master->dev);
> +
> +	if (pdev->ats_enabled)

If the master->ats_enabled check above passes when ATS isn't actually 
enabled, surely that's a bug?

Robin.

> +		pci_disable_ats(pdev);
> +
>   	/*
>   	 * Ensure ATS is disabled at the endpoint before we issue the
>   	 * ATC invalidation via the SMMU.
> @@ -2453,8 +2458,7 @@ static int arm_smmu_attach_dev(struct iommu_domain *domain, struct device *dev)
>   
>   	master->domain = smmu_domain;
>   
> -	if (smmu_domain->stage != ARM_SMMU_DOMAIN_BYPASS)
> -		master->ats_enabled = arm_smmu_ats_supported(master);
> +	master->ats_enabled = arm_smmu_ats_supported(master);
>   
>   	arm_smmu_install_ste_for_dev(master);
>