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SubjectRe: [PATCH v5 4/7] PCI/ATS: Add PRI support for PCIe VF devices
On Thu, Aug 01, 2019 at 05:06:01PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>
> When IOMMU tries to enable Page Request Interface (PRI) for VF device
> in iommu_enable_dev_iotlb(), it always fails because PRI support for
> PCIe VF device is currently broken. 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
> PRI of the PF and not implement it. Hence we need to create exception
> for handling the PRI support for PCIe VF device.
>
> Also, since PRI is a shared resource between PF/VF, following rules
> should apply.
>
> 1. Use proper locking before accessing/modifying PF resources in VF
> PRI enable/disable call.
> 2. Use reference count logic to track the usage of PRI resource.
> 3. Disable PRI only if the PRI reference count (pri_ref_cnt) is zero.
>
> 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 | 143 ++++++++++++++++++++++++++++++++++----------
> include/linux/pci.h | 2 +
> 2 files changed, 112 insertions(+), 33 deletions(-)
>
> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
> index 1f4be27a071d..079dc5444444 100644
> --- a/drivers/pci/ats.c
> +++ b/drivers/pci/ats.c
> @@ -189,6 +189,8 @@ void pci_pri_init(struct pci_dev *pdev)
> if (pdev->is_virtfn)
> return;
>
> + mutex_init(&pdev->pri_lock);
> +
> pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
> if (!pos)
> return;
> @@ -221,29 +223,57 @@ int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
> {
> u16 control, status;
> u32 max_requests;
> + int ret = 0;
> + struct pci_dev *pf = pci_physfn(pdev);
>
> - if (WARN_ON(pdev->pri_enabled))
> - return -EBUSY;
> + mutex_lock(&pf->pri_lock);
>
> - if (!pdev->pri_cap)
> - return -EINVAL;
> + if (WARN_ON(pdev->pri_enabled)) {
> + ret = -EBUSY;
> + goto pri_unlock;
> + }
>
> - pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
> - if (!(status & PCI_PRI_STATUS_STOPPED))
> - return -EBUSY;
> + if (!pf->pri_cap) {
> + ret = -EINVAL;
> + goto pri_unlock;
> + }
> +
> + if (pdev->is_virtfn && pf->pri_enabled)
> + goto update_status;
> +
> + /*
> + * Before updating PRI registers, make sure there is no
> + * outstanding PRI requests.
> + */
> + pci_read_config_word(pf, pf->pri_cap + PCI_PRI_STATUS, &status);
> + if (!(status & PCI_PRI_STATUS_STOPPED)) {
> + ret = -EBUSY;
> + goto pri_unlock;
> + }
>
> - pci_read_config_dword(pdev, pdev->pri_cap + PCI_PRI_MAX_REQ,
> - &max_requests);
> + pci_read_config_dword(pf, pf->pri_cap + PCI_PRI_MAX_REQ, &max_requests);
> reqs = min(max_requests, reqs);
> - pdev->pri_reqs_alloc = reqs;
> - pci_write_config_dword(pdev, pdev->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
> + pf->pri_reqs_alloc = reqs;
> + pci_write_config_dword(pf, pf->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
>
> control = PCI_PRI_CTRL_ENABLE;
> - pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
> + pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
>
> - pdev->pri_enabled = 1;
> + /*
> + * If PRI is not already enabled in PF, increment the PF
> + * pri_ref_cnt to track the usage of PRI interface.
> + */
> + if (pdev->is_virtfn && !pf->pri_enabled) {
> + atomic_inc(&pf->pri_ref_cnt);
> + pf->pri_enabled = 1;
> + }
>
> - return 0;
> +update_status:
> + atomic_inc(&pf->pri_ref_cnt);
> + pdev->pri_enabled = 1;
> +pri_unlock:
> + mutex_unlock(&pf->pri_lock);
> + return ret;
> }
> EXPORT_SYMBOL_GPL(pci_enable_pri);
>
> @@ -256,18 +286,30 @@ EXPORT_SYMBOL_GPL(pci_enable_pri);
> void pci_disable_pri(struct pci_dev *pdev)
> {
> u16 control;
> + struct pci_dev *pf = pci_physfn(pdev);
>
> - if (WARN_ON(!pdev->pri_enabled))
> - return;
> + mutex_lock(&pf->pri_lock);
>
> - if (!pdev->pri_cap)
> - return;
> + if (WARN_ON(!pdev->pri_enabled) || !pf->pri_cap)
> + goto pri_unlock;
> +
> + atomic_dec(&pf->pri_ref_cnt);
>
> - pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, &control);
> + /*
> + * If pri_ref_cnt is not zero, then don't modify hardware
> + * registers.
> + */
> + if (atomic_read(&pf->pri_ref_cnt))
> + goto done;
> +
> + pci_read_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, &control);
> control &= ~PCI_PRI_CTRL_ENABLE;
> - pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
> + pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
>
> +done:
> pdev->pri_enabled = 0;
> +pri_unlock:
> + mutex_unlock(&pf->pri_lock);
> }
> EXPORT_SYMBOL_GPL(pci_disable_pri);
>
> @@ -277,17 +319,31 @@ EXPORT_SYMBOL_GPL(pci_disable_pri);
> */
> void pci_restore_pri_state(struct pci_dev *pdev)
> {
> - u16 control = PCI_PRI_CTRL_ENABLE;
> - u32 reqs = pdev->pri_reqs_alloc;
> + u16 control;
> + u32 reqs;
> + struct pci_dev *pf = pci_physfn(pdev);
>
> if (!pdev->pri_enabled)
> return;
>
> - if (!pdev->pri_cap)
> + if (!pf->pri_cap)
> return;
>
> - pci_write_config_dword(pdev, pdev->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
> - pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
> + mutex_lock(&pf->pri_lock);
> +
> + /* If PRI is already enabled by other VF's or PF, return */
> + pci_read_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, &control);
> + if (control & PCI_PRI_CTRL_ENABLE)
> + goto pri_unlock;
> +
> + reqs = pf->pri_reqs_alloc;
> + control = PCI_PRI_CTRL_ENABLE;
> +
> + pci_write_config_dword(pf, pf->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
> + pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
> +
> +pri_unlock:
> + mutex_unlock(&pf->pri_lock);
> }
> EXPORT_SYMBOL_GPL(pci_restore_pri_state);
>
> @@ -300,18 +356,32 @@ EXPORT_SYMBOL_GPL(pci_restore_pri_state);
> */
> int pci_reset_pri(struct pci_dev *pdev)
> {
> + struct pci_dev *pf = pci_physfn(pdev);
> u16 control;
> + int ret = 0;
>
> - if (WARN_ON(pdev->pri_enabled))
> - return -EBUSY;
> + mutex_lock(&pf->pri_lock);
>
> - if (!pdev->pri_cap)
> - return -EINVAL;
> + if (WARN_ON(pdev->pri_enabled)) {
> + ret = -EBUSY;
> + goto done;
> + }
> +
> + if (!pf->pri_cap) {
> + ret = -EINVAL;
> + goto done;
> + }
> +
> + /* If PRI is already enabled by other VF's or PF, return 0 */
> + if (pf->pri_enabled)
> + goto done;
>
> control = PCI_PRI_CTRL_RESET;
> - pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
>
> - return 0;
> + pci_write_config_word(pf, pf->pri_cap + PCI_PRI_CTRL, control);
> +done:
> + mutex_unlock(&pf->pri_lock);
> + return ret;
> }
> EXPORT_SYMBOL_GPL(pci_reset_pri);
> #endif /* CONFIG_PCI_PRI */
> @@ -475,11 +545,18 @@ EXPORT_SYMBOL_GPL(pci_pasid_features);
> int pci_prg_resp_pasid_required(struct pci_dev *pdev)
> {
> u16 status;
> + struct pci_dev *pf = pci_physfn(pdev);
> +
> + mutex_lock(&pf->pri_lock);

I don't believe this lock is necessary. What is it protecting?

We're only doing a single read of PCI_PRI_STATUS here, and with the
lock, we'll read it either before or after the critical sections in
pci_enable_pri(), pci_disable_pri(), pci_restore_pri_state(), and
pci_reset_pri().

And without the lock, we'll *also* read PCI_PRI_STATUS either before
or after anything in those functions that affects it.

> - if (!pdev->pri_cap)
> + if (!pf->pri_cap) {
> + mutex_unlock(&pf->pri_lock);
> return 0;
> + }
> +
> + pci_read_config_word(pf, pf->pri_cap + PCI_PRI_STATUS, &status);
>
> - pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
> + mutex_unlock(&pf->pri_lock);
>
> if (status & PCI_PRI_STATUS_PASID)
> return 1;
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 27224c0db849..3c9c4c82be27 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -455,8 +455,10 @@ struct pci_dev {
> atomic_t ats_ref_cnt; /* Number of VFs with ATS enabled */
> #endif
> #ifdef CONFIG_PCI_PRI
> + struct mutex pri_lock; /* PRI enable lock */
> u16 pri_cap; /* PRI Capability offset */
> u32 pri_reqs_alloc; /* Number of PRI requests allocated */
> + atomic_t pri_ref_cnt; /* Number of PF/VF PRI users */
> #endif
> #ifdef CONFIG_PCI_PASID
> u16 pasid_cap; /* PASID Capability offset */
> --
> 2.21.0
>

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