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SubjectRe: [PATCH v2 1/5] PCI/ATS: Add PRI support for PCIe VF devices
On Mon, May 06, 2019 at 10:20:03AM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>
> When IOMMU tries to enable PRI for VF device in
> iommu_enable_dev_iotlb(), it always fails because PRI support for PCIe
> VF device is currently broken in PCIE driver. Current implementation
> expects the given PCIe device (PF & VF) to implement PRI capability
> before enabling the PRI support. But this assumption is incorrect. As
> per PCIe spec r4.0, sec 9.3.7.11, all VFs associated with PF can only
> use the Page Request Interface (PRI) of the PF and not implement it.
> Hence we need to create exception for handling the PRI support for PCIe
> VF device.
>
> Since PRI is shared between PF/VF devices, following rules should apply.
>
> 1. Enable PRI in VF only if its already enabled in PF.
> 2. When enabling/disabling PRI for VF, instead of configuring the
> registers just increase/decrease the usage count (pri_ref_cnt) of PF.
> 3. Disable PRI in PF only if pr_ref_cnt is zero.

s/pr_ref_cnt/pri_ref_cnt/

> 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 | 53 +++++++++++++++++++++++++++++++++++++++++++--
> include/linux/pci.h | 1 +
> 2 files changed, 52 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index 97c08146534a..5582e5d83a3f 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -181,12 +181,39 @@ int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
> u16 control, status;
> u32 max_requests;
> int pos;
> + struct pci_dev *pf;
>
> if (WARN_ON(pdev->pri_enabled))
> return -EBUSY;
>
> pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
> - if (!pos)
> +
> + if (pdev->is_virtfn) {
> + /*
> + * Per PCIe r4.0, sec 9.3.7.11, VF must not implement PRI
> + * Capability.
> + */
> + if (pos) {
> + dev_err(&pdev->dev, "VF must not implement PRI");
> + return -EINVAL;
> + }

This seems gratuitous. It finds implementation errors, but since we
correctly use the PF here anyway, it doesn't *need* to prevent PRI on
the VF from working.

I think you should just have:

if (pdev->is_virtfn) {
pf = pci_physfn(pdev);
if (!pf->pri_enabled)
return -EINVAL;

pdev->pri_enabled = 1;
atomic_inc(&pf->pri_ref_cnt);
}

pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
if (!pos)
return -EINVAL;

> + pf = pci_physfn(pdev);
> +
> + /* If VF config does not match with PF, return error */
> + if (!pf->pri_enabled)
> + return -EINVAL;
> +
> + pdev->pri_reqs_alloc = pf->pri_reqs_alloc;

Is there any point in setting vf->pri_reqs_alloc? I don't think it's
used for anything since pri_reqs_alloc is only used to write the PF
capability, and we only do that for the PF.

> + pdev->pri_enabled = 1;
> +
> + /* Increment PF PRI refcount */

Superfluous comment, since that's exactly what the code says. It's
always good when the code is so clear that it doesn't require comments :)

> + atomic_inc(&pf->pri_ref_cnt);
> +
> + return 0;
> + }
> +
> + if (pdev->is_physfn && !pos)
> return -EINVAL;
>
> pci_read_config_word(pdev, pos + PCI_PRI_STATUS, &status);
> @@ -202,7 +229,6 @@ int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
> pci_write_config_word(pdev, pos + PCI_PRI_CTRL, control);
>
> pdev->pri_enabled = 1;
> -
> return 0;
> }
> EXPORT_SYMBOL_GPL(pci_enable_pri);
> @@ -217,10 +243,27 @@ void pci_disable_pri(struct pci_dev *pdev)
> {
> u16 control;
> int pos;
> + struct pci_dev *pf;
>
> if (WARN_ON(!pdev->pri_enabled))
> return;
>
> + /* All VFs should be disabled before disabling PF */
> + if (atomic_read(&pdev->pri_ref_cnt))
> + return;
> +
> + if (pdev->is_virtfn) {
> + /* Since VF shares PRI with PF, use PF config. */
> + pf = pci_physfn(pdev);
> +
> + /* Decrement PF PRI refcount */
> + atomic_dec(&pf->pri_ref_cnt);
> +
> + pdev->pri_enabled = 0;
> +
> + return;
> + }
> +
> pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
> if (!pos)
> return;
> @@ -246,6 +289,9 @@ void pci_restore_pri_state(struct pci_dev *pdev)
> if (!pdev->pri_enabled)
> return;
>
> + if (pdev->is_virtfn)
> + return;
> +
> pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
> if (!pos)
> return;
> @@ -270,6 +316,9 @@ int pci_reset_pri(struct pci_dev *pdev)
> if (WARN_ON(pdev->pri_enabled))
> return -EBUSY;
>
> + if (pdev->is_virtfn)
> + return 0;
> +
> pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
> if (!pos)
> return -EINVAL;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 77448215ef5b..699c79c99a39 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -450,6 +450,7 @@ struct pci_dev {
> #endif
> #ifdef CONFIG_PCI_PRI
> u32 pri_reqs_alloc; /* Number of PRI requests allocated */
> + atomic_t pri_ref_cnt; /* Number of VFs with PRI enabled */
> #endif
> #ifdef CONFIG_PCI_PASID
> u16 pasid_features;
> --
> 2.20.1
>

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