Re: [PATCH 8/8] iommu/arm-smmu-v3: Add support for PCI PASID

Auger Eric
2019-07-08T07:58:25Z

Hi Jean,

On 6/10/19 8:47 PM, Jean-Philippe Brucker wrote:
> Enable PASID for PCI devices that support it. Since the SSID tables are
> allocated by arm_smmu_attach_dev(), PASID has to be enabled early enough.
> arm_smmu_dev_feature_enable() would be too late, since by that time the
> main DMA domain has already been attached. Do it in add_device() instead.
>
> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
> ---
> drivers/iommu/arm-smmu-v3.c | 51 ++++++++++++++++++++++++++++++++++++-
> 1 file changed, 50 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index 972bfb80f964..a8a516d9ff10 100644
> --- a/drivers/iommu/arm-smmu-v3.c
> +++ b/drivers/iommu/arm-smmu-v3.c
> @@ -2197,6 +2197,49 @@ static void arm_smmu_disable_ats(struct arm_smmu_master *master)
> master->ats_enabled = false;
> }
>
> +static int arm_smmu_enable_pasid(struct arm_smmu_master *master)
> +{
> + int ret;
> + int features;
> + int num_pasids;
> + struct pci_dev *pdev;
> +
> + if (!dev_is_pci(master->dev))
> + return -ENOSYS;
> +
> + pdev = to_pci_dev(master->dev);
> +
> + features = pci_pasid_features(pdev);
> + if (features < 0)
> + return -ENOSYS;
> +
> + num_pasids = pci_max_pasids(pdev);
> + if (num_pasids <= 0)
> + return -ENOSYS;
> +
> + ret = pci_enable_pasid(pdev, features);
> + if (!ret)
> + master->ssid_bits = min_t(u8, ilog2(num_pasids),
> + master->smmu->ssid_bits);
I don't really get why this setting is conditional to the success of
pci_enabled_pasid and not num_pasids > 0.

If it fails the ssid_bits is set to min(smmu->ssid_bits,
fwspec->num_pasid_bits) anyway.

> + return ret;
> +}
> +
> +static void arm_smmu_disable_pasid(struct arm_smmu_master *master)
> +{
> + struct pci_dev *pdev;
> +
> + if (!dev_is_pci(master->dev))
> + return;
> +
> + pdev = to_pci_dev(master->dev);
> +
> + if (!pdev->pasid_enabled)
> + return;
> +
> + pci_disable_pasid(pdev);
> + master->ssid_bits = 0;
in case of a platform device you leave the ssid_bits to a value != 0. Is
that what you want?
> +}
> +
> static void arm_smmu_detach_dev(struct arm_smmu_master *master)
> {
> unsigned long flags;
> @@ -2413,6 +2456,9 @@ static int arm_smmu_add_device(struct device *dev)
>
> master->ssid_bits = min(smmu->ssid_bits, fwspec->num_pasid_bits);
>
> + /* Note that PASID must be enabled before, and disabled after ATS */
> + arm_smmu_enable_pasid(master);
In case the call fails, don't you want to handle the error and reset the
ssid_bits?
> +
> /*
> * If the SMMU doesn't support 2-stage CD, limit the linear
> * tables to a reasonable number of contexts, let's say
> @@ -2423,7 +2469,7 @@ static int arm_smmu_add_device(struct device *dev)
>
> ret = iommu_device_link(&smmu->iommu, dev);
> if (ret)
> - goto err_free_master;
> + goto err_disable_pasid;
>
> group = iommu_group_get_for_dev(dev);
> if (IS_ERR(group)) {
> @@ -2436,6 +2482,8 @@ static int arm_smmu_add_device(struct device *dev)
>
> err_unlink:
> iommu_device_unlink(&smmu->iommu, dev);
> +err_disable_pasid:
> + arm_smmu_disable_pasid(master);
> err_free_master:
> kfree(master);
> fwspec->iommu_priv = NULL;
> @@ -2456,6 +2504,7 @@ static void arm_smmu_remove_device(struct device *dev)
> arm_smmu_detach_dev(master);
> iommu_group_remove_device(dev);
> iommu_device_unlink(&smmu->iommu, dev);
> + arm_smmu_disable_pasid(master);
> kfree(master);
> iommu_fwspec_free(dev);
> }
>
Thanks

Eric