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Date: Wed, 29 May 2019 16:04:27 -0700
From: "Raj, Ashok" <ashok.raj@...el.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: sathyanarayanan.kuppuswamy@...ux.intel.com,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
keith.busch@...el.com, Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v2 1/5] PCI/ATS: Add PRI support for PCIe VF devices
On Wed, May 29, 2019 at 05:57:14PM -0500, Bjorn Helgaas wrote:
> On Mon, May 06, 2019 at 10:20:03AM -0700, sathyanarayanan.kuppuswamy@...ux.intel.com wrote:
> > From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.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@...el.com>
> > Cc: Keith Busch <keith.busch@...el.com>
> > Suggested-by: Ashok Raj <ashok.raj@...el.com>
> > Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.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;
This would be incorrect. Since if we never did any bind_mm to the PF
PRI would not have been enabled. Currently this is done in the IOMMU
driver, and not in the device driver.
I suppose we should enable PF capability if its not enabled. Same
comment would be applicable for PASID as well.
>
> 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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