Re: [PATCH v2 2/5] PCI/ATS: Add PASID support for PCIe VF devices

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, May 06, 2019 at 10:20:04AM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> 
> When IOMMU tries to enable PASID for VF device in
> iommu_enable_dev_iotlb(), it always fails because PASID support for PCIe
> VF device is currently broken in PCIE driver. Current implementation
> expects the given PCIe device (PF & VF) to implement PASID capability
> before enabling the PASID support. But this assumption is incorrect. As
> per PCIe spec r4.0, sec 9.3.7.14, all VFs associated with PF can only
> use the PASID of the PF and not implement it.
> 
> Since PASID is shared between PF/VF devices, following rules should
> apply.
> 
> 1. Enable PASID in VF only if its already enabled in PF.

s/its/it's/ (same comment applies to PRI patch, IIRC)

> 2. Enable PASID in VF only if the requested features matches with PF
> config, otherwise return error.
> 3. When enabling/disabling PASID for VF, instead of configuring the PF
> registers just increase/decrease the usage count (pasid_ref_cnt).
> 4. Disable PASID in PF (configuring the registers) only if pasid_ref_cnt
> is zero.
> 5. When reading PASID features/settings for VF, use registers of
> corresponding PF.
> 
> Cc: Ashok Raj <ashok.raj@intel.com>
> Cc: Keith Busch <keith.busch@intel.com>
> Suggested-by: Ashok Raj <ashok.raj@intel.com>
> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
> ---
>  drivers/pci/ats.c   | 55 ++++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/pci.h |  1 +
>  2 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index 5582e5d83a3f..e7a904e347c3 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -345,6 +345,7 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
>  {
>  	u16 control, supported;
>  	int pos;
> +	struct pci_dev *pf;
>  
>  	if (WARN_ON(pdev->pasid_enabled))
>  		return -EBUSY;
> @@ -353,7 +354,33 @@ int pci_enable_pasid(struct pci_dev *pdev, int features)
>  		return -EINVAL;
>  
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
> -	if (!pos)
> +
> +	if (pdev->is_virtfn) {
> +		/*
> +		 * Per PCIe r4.0, sec 9.3.7.14, VF must not implement
> +		 * Process Address Space ID (PASID) Capability.
> +		*/
> +		if (pos) {
> +			dev_err(&pdev->dev, "VF must not implement PASID\n");
> +			return -EINVAL
> +		}

Same comment as for PRI.

> +		/* Since VF shares PASID with PF, use PF config */
> +		pf = pci_physfn(pdev);
> +
> +		/* If VF config does not match with PF, return error */
> +		if (!pf->pasid_enabled || pf->pasid_features != features)
> +			return -EINVAL;
> +
> +		pdev->pasid_features = features;

I don't think this is used for VFs.

> +		pdev->pasid_enabled = 1;
> +
> +		/* Increment PF PASID refcount */
> +		atomic_inc(&pf->pasid_ref_cnt);
> +
> +		return 0;
> +	}
> +
> +	if (pdev->is_physfn && !pos)
>  		return -EINVAL;
>  
>  	pci_read_config_word(pdev, pos + PCI_PASID_CAP, &supported);
> @@ -382,10 +409,27 @@ void pci_disable_pasid(struct pci_dev *pdev)
>  {
>  	u16 control = 0;
>  	int pos;
> +	struct pci_dev *pf;
>  
>  	if (WARN_ON(!pdev->pasid_enabled))
>  		return;
>  
> +	/* All VFs PASID should be disabled before disabling PF PASID*/

Add space at end of comment.

> +	if (atomic_read(&pdev->pasid_ref_cnt))
> +		return;
> +
> +	if (pdev->is_virtfn) {
> +		/* Since VF shares PASID with PF, use PF config. */

Most single-line, single-sentence comments here do not include a
trailing period.

> +		pf = pci_physfn(pdev);
> +
> +		/* Decrement PF PASID refcount */
> +		atomic_dec(&pf->pasid_ref_cnt);
> +
> +		pdev->pasid_enabled = 0;
> +
> +		return;
> +	}
> +
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
>  	if (!pos)
>  		return;
> @@ -408,6 +452,9 @@ void pci_restore_pasid_state(struct pci_dev *pdev)
>  	if (!pdev->pasid_enabled)
>  		return;
>  
> +	if (pdev->is_virtfn)
> +		return;
> +
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
>  	if (!pos)
>  		return;
> @@ -432,6 +479,9 @@ int pci_pasid_features(struct pci_dev *pdev)
>  	u16 supported;
>  	int pos;
>  
> +	if (pdev->is_virtfn)
> +		pdev = pci_physfn(pdev);
> +
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
>  	if (!pos)
>  		return -EINVAL;
> @@ -488,6 +538,9 @@ int pci_max_pasids(struct pci_dev *pdev)
>  	u16 supported;
>  	int pos;
>  
> +	if (pdev->is_virtfn)
> +		pdev = pci_physfn(pdev);
> +
>  	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
>  	if (!pos)
>  		return -EINVAL;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 699c79c99a39..2a761ea63f8d 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -454,6 +454,7 @@ struct pci_dev {
>  #endif
>  #ifdef CONFIG_PCI_PASID
>  	u16		pasid_features;
> +	atomic_t	pasid_ref_cnt;	/* Number of VFs with PASID enabled */
>  #endif
>  #ifdef CONFIG_PCI_P2PDMA
>  	struct pci_p2pdma *p2pdma;
> -- 
> 2.20.1
>