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    SubjectRe: [PATCH v5 5/7] PCI/ATS: Add PASID support for PCIe VF devices
    On Thu, Aug 15, 2019 at 12:04:30AM -0500, Bjorn Helgaas wrote:
    > On Tue, Aug 13, 2019 at 03:19:58PM -0700, Kuppuswamy Sathyanarayanan wrote:
    > > On Mon, Aug 12, 2019 at 03:05:08PM -0500, Bjorn Helgaas wrote:
    > > > On Thu, Aug 01, 2019 at 05:06:02PM -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.
    > > > >
    > > > > Also, since PASID is a shared resource between PF/VF, following rules
    > > > > should apply.
    > > > >
    > > > > 1. Use proper locking before accessing/modifying PF resources in VF
    > > > > PASID enable/disable call.
    > > > > 2. Use reference count logic to track the usage of PASID resource.
    > > > > 3. Disable PASID only if the PASID reference count (pasid_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 | 113 ++++++++++++++++++++++++++++++++++----------
    > > > > include/linux/pci.h | 2 +
    > > > > 2 files changed, 90 insertions(+), 25 deletions(-)
    > > > >
    > > > > diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
    > > > > index 079dc5444444..9384afd7d00e 100644
    > > > > --- a/drivers/pci/ats.c
    > > > > +++ b/drivers/pci/ats.c
    > > > > @@ -402,6 +402,8 @@ void pci_pasid_init(struct pci_dev *pdev)
    > > > > if (pdev->is_virtfn)
    > > > > return;
    > > > >
    > > > > + mutex_init(&pdev->pasid_lock);
    > > > > +
    > > > > pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PASID);
    > > > > if (!pos)
    > > > > return;
    > > > > @@ -436,32 +438,57 @@ void pci_pasid_init(struct pci_dev *pdev)
    > > > > int pci_enable_pasid(struct pci_dev *pdev, int features)
    > > > > {
    > > > > u16 control, supported;
    > > > > + int ret = 0;
    > > > > + struct pci_dev *pf = pci_physfn(pdev);
    > > > >
    > > > > - if (WARN_ON(pdev->pasid_enabled))
    > > > > - return -EBUSY;
    > > > > + mutex_lock(&pf->pasid_lock);
    > > > >
    > > > > - if (!pdev->eetlp_prefix_path)
    > > > > - return -EINVAL;
    > > > > + if (WARN_ON(pdev->pasid_enabled)) {
    > > > > + ret = -EBUSY;
    > > > > + goto pasid_unlock;
    > > > > + }
    > > > >
    > > > > - if (!pdev->pasid_cap)
    > > > > - return -EINVAL;
    > > > > + if (!pdev->eetlp_prefix_path) {
    > > > > + ret = -EINVAL;
    > > > > + goto pasid_unlock;
    > > > > + }
    > > > >
    > > > > - pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
    > > > > - &supported);
    > > > > + if (!pf->pasid_cap) {
    > > > > + ret = -EINVAL;
    > > > > + goto pasid_unlock;
    > > > > + }
    > > > > +
    > > > > + if (pdev->is_virtfn && pf->pasid_enabled)
    > > > > + goto update_status;
    > > > > +
    > > > > + pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP, &supported);
    > > > > supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
    > > > >
    > > > > /* User wants to enable anything unsupported? */
    > > > > - if ((supported & features) != features)
    > > > > - return -EINVAL;
    > > > > + if ((supported & features) != features) {
    > > > > + ret = -EINVAL;
    > > > > + goto pasid_unlock;
    > > > > + }
    > > > >
    > > > > control = PCI_PASID_CTRL_ENABLE | features;
    > > > > - pdev->pasid_features = features;
    > > > > -
    > > > > + pf->pasid_features = features;
    > > > > pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
    > > > >
    > > > > - pdev->pasid_enabled = 1;
    > > > > + /*
    > > > > + * If PASID is not already enabled in PF, increment pasid_ref_cnt
    > > > > + * to count PF PASID usage.
    > > > > + */
    > > > > + if (pdev->is_virtfn && !pf->pasid_enabled) {
    > > > > + atomic_inc(&pf->pasid_ref_cnt);
    > > > > + pf->pasid_enabled = 1;
    > > > > + }
    > > > >
    > > > > - return 0;
    > > > > +update_status:
    > > > > + atomic_inc(&pf->pasid_ref_cnt);
    > > > > + pdev->pasid_enabled = 1;
    > > > > +pasid_unlock:
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > + return ret;
    > > > > }
    > > > > EXPORT_SYMBOL_GPL(pci_enable_pasid);
    > > > >
    > > > > @@ -472,16 +499,29 @@ EXPORT_SYMBOL_GPL(pci_enable_pasid);
    > > > > void pci_disable_pasid(struct pci_dev *pdev)
    > > > > {
    > > > > u16 control = 0;
    > > > > + struct pci_dev *pf = pci_physfn(pdev);
    > > > > +
    > > > > + mutex_lock(&pf->pasid_lock);
    > > > >
    > > > > if (WARN_ON(!pdev->pasid_enabled))
    > > > > - return;
    > > > > + goto pasid_unlock;
    > > > >
    > > > > - if (!pdev->pasid_cap)
    > > > > - return;
    > > > > + if (!pf->pasid_cap)
    > > > > + goto pasid_unlock;
    > > > >
    > > > > - pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
    > > > > + atomic_dec(&pf->pasid_ref_cnt);
    > > > >
    > > > > + if (atomic_read(&pf->pasid_ref_cnt))
    > > > > + goto done;
    > > > > +
    > > > > + /* Disable PASID only if pasid_ref_cnt is zero */
    > > > > + pci_write_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, control);
    > > > > +
    > > > > +done:
    > > > > pdev->pasid_enabled = 0;
    > > > > +pasid_unlock:
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > +
    > > > > }
    > > > > EXPORT_SYMBOL_GPL(pci_disable_pasid);
    > > > >
    > > > > @@ -492,15 +532,25 @@ EXPORT_SYMBOL_GPL(pci_disable_pasid);
    > > > > void pci_restore_pasid_state(struct pci_dev *pdev)
    > > > > {
    > > > > u16 control;
    > > > > + struct pci_dev *pf = pci_physfn(pdev);
    > > > >
    > > > > if (!pdev->pasid_enabled)
    > > > > return;
    > > > >
    > > > > - if (!pdev->pasid_cap)
    > > > > + if (!pf->pasid_cap)
    > > > > return;
    > > > >
    > > > > + mutex_lock(&pf->pasid_lock);
    > > > > +
    > > > > + pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, &control);
    > > > > + if (control & PCI_PASID_CTRL_ENABLE)
    > > > > + goto pasid_unlock;
    > > > > +
    > > > > control = PCI_PASID_CTRL_ENABLE | pdev->pasid_features;
    > > > > - pci_write_config_word(pdev, pdev->pasid_cap + PCI_PASID_CTRL, control);
    > > > > + pci_write_config_word(pf, pf->pasid_cap + PCI_PASID_CTRL, control);
    > > > > +
    > > > > +pasid_unlock:
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > }
    > > > > EXPORT_SYMBOL_GPL(pci_restore_pasid_state);
    > > > >
    > > > > @@ -517,15 +567,22 @@ EXPORT_SYMBOL_GPL(pci_restore_pasid_state);
    > > > > int pci_pasid_features(struct pci_dev *pdev)
    > > > > {
    > > > > u16 supported;
    > > > > + struct pci_dev *pf = pci_physfn(pdev);
    > > > > +
    > > > > + mutex_lock(&pf->pasid_lock);
    > > > >
    > > > > - if (!pdev->pasid_cap)
    > > > > + if (!pf->pasid_cap) {
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > return -EINVAL;
    > > > > + }
    > > > >
    > > > > - pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
    > > > > + pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP,
    > > > > &supported);
    > > > >
    > > > > supported &= PCI_PASID_CAP_EXEC | PCI_PASID_CAP_PRIV;
    > > > >
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > +
    > > > > return supported;
    > > > > }
    > > > > EXPORT_SYMBOL_GPL(pci_pasid_features);
    > > > > @@ -579,15 +636,21 @@ EXPORT_SYMBOL_GPL(pci_prg_resp_pasid_required);
    > > > > int pci_max_pasids(struct pci_dev *pdev)
    > > > > {
    > > > > u16 supported;
    > > > > + struct pci_dev *pf = pci_physfn(pdev);
    > > > > +
    > > > > + mutex_lock(&pf->pasid_lock);
    > > > >
    > > > > - if (!pdev->pasid_cap)
    > > > > + if (!pf->pasid_cap) {
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > return -EINVAL;
    > > > > + }
    > > > >
    > > > > - pci_read_config_word(pdev, pdev->pasid_cap + PCI_PASID_CAP,
    > > > > - &supported);
    > > > > + pci_read_config_word(pf, pf->pasid_cap + PCI_PASID_CAP, &supported);
    > > > >
    > > > > supported = (supported & PASID_NUMBER_MASK) >> PASID_NUMBER_SHIFT;
    > > > >
    > > > > + mutex_unlock(&pf->pasid_lock);
    > > > > +
    > > > > return (1 << supported);
    > > > > }
    > > > > EXPORT_SYMBOL_GPL(pci_max_pasids);
    > > > > diff --git a/include/linux/pci.h b/include/linux/pci.h
    > > > > index 3c9c4c82be27..4bfcca045afd 100644
    > > > > --- a/include/linux/pci.h
    > > > > +++ b/include/linux/pci.h
    > > > > @@ -461,8 +461,10 @@ struct pci_dev {
    > > > > atomic_t pri_ref_cnt; /* Number of PF/VF PRI users */
    > > > > #endif
    > > > > #ifdef CONFIG_PCI_PASID
    > > > > + struct mutex pasid_lock; /* PASID enable lock */
    > > >
    > > > I think these locks are finer-grained than necessary. I'm not sure
    > > > it's worth having two mutexes for every device (one for PRI and
    > > > another for PASID). Is there really a performance benefit for having
    > > > two?
    >
    > > Performance benefit should be minimal. But, PRI and PASID are functionally
    > > independent. So I don't think its correct to protect its resources with
    > > a common lock. Let me know your comments.
    >
    > I'm not an expert on PRI and PASID, but if we can figure out a place
    > to put it and a way to manage it, I think it's OK to have a lock that
    > protects both. I'm thinking about the size of the pci_dev -- I'm not
    > sure the benefit of having two locks is commensurate with the size
    > cost.
    >
    > > > Do it (or do they) need to be in struct pci_dev? You only use the PF
    > > > mutexes, so maybe it could be in the struct pci_sriov, which I think
    > > > is only one per PF.
    >
    > > Its possible to move it to pci_sriov structure. But is that the right
    > > place for it? This lock is only used for protecting PRI and PASID feature
    > > updates and PRI/PASID are not dependent on IOV feature. Let me know your
    > > comments.
    >
    > Hmm. I misunderstood the use of these. I had the impression they
    > were only used for PFs. If that were the case, pci_sriov might make
    > sense because we only allocate that for PFs (when we enable SR-IOV in
    > sriov_init()). But IIUC that's *not* the case: even non-SR-IOV
    > devices can use PRI/PASID; it's just that if a *VF* uses them, the VF
    > is actually using the PRI of the PF.
    Yes, your current interpretation is correct. Even non SR-IOV devices can
    use PRI/PASID. But the race condition issue only exists in SR-IOV
    (PF/VF) devices.
    >
    > > If you want to move this lock to pci_sriov structure and use one lock
    > > for both PRI/PASID, then the implementation would look like following. We
    > > could create physfn lock/unlock functions in include/linux/pci.h similar
    > > to pci_physfn() function.
    >
    > > #ifdef CONFIG_PCI_IOV
    > > static inline void pci_physfn_reslock(struct pci_dev *dev)
    > > {
    > > struct pci_dev *pf = pci_physfn(dev);
    > >
    > > if (!pf->is_physfn)
    > > return;
    > >
    > > mutex_lock(&pf->sriov->reslock);
    > >
    > > }
    > > #else
    > > static inline void pci_physfn_reslock(struct pci_dev *dev) {};
    > > #endif
    >
    > Yeah, that's not a pretty solution. IIUC, we don't need to lock at
    > all for non-SR-IOV devices, because we're operating on our own device
    > and nobody else should be touching it. Right?
    Yes, we don't need to lock for non-SR-IOV devices.
    >
    > Only the SR-IOV case (operating on a PF with SR-IOV enabled or on one
    > of its VFs) needs locking because these are all sharing one resource.
    >
    > So it's kind of a shame to allocate the lock for *every* pci_dev, when
    > we only need it for PFs with SR-IOV enabled.
    if not pci_dev structure, then next appropriate place to add this lock
    is struct pci_sriov.
    Since the issue is specific to SR-IOV devices, even if PASID/PRI has no
    dependency on SR-IOV, I think the we can add the reslock to pci_sriov
    structure. Please check the attached patch for sample implementation.
    >
    > Bjorn

    --
    --
    Sathyanarayanan Kuppuswamy
    Linux kernel developer
    From 7ef4ea0e5ef761286602daac5b6913ad610e37ce Mon Sep 17 00:00:00 2001
    From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    Date: Thu, 15 Aug 2019 17:34:06 -0700
    Subject: [PATCH v1 1/1] PCI/IOV: Add pci_physfn_reslock/unlock() interfaces

    As per PCIe spec r5.0, sec 9.3.7, in SR-IOV devices, capabilities like
    PASID, PRI, VC, etc are shared between PF and its associated VFs. So, to
    prevent race conditions between PF/VF while updating configuration
    registers of these shared capabilities, a new synchronization mechanism
    is required.

    As a first step, create shared resource lock and expose expose
    pci_physfn_reslock/unlock() API's. Users of these shared capabilities can
    use these lock/unlock interfaces to synchronize its access.

    Since the shared capability is always implemented by PF, reslock mutex
    has been added to pci_sriov structure which only exists for PF.

    NOTE: Currently this reslock is common for all shared capabilities
    between PF/VF. In future, if any performance impact has been noticed, we
    should create individual locks for each of the shared capability.

    Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
    ---
    drivers/pci/iov.c | 1 +
    drivers/pci/pci.h | 40 ++++++++++++++++++++++++++++++++++++++++
    2 files changed, 41 insertions(+)

    diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
    index 525fd3f272b3..004e7076b065 100644
    --- a/drivers/pci/iov.c
    +++ b/drivers/pci/iov.c
    @@ -507,6 +507,7 @@ static int sriov_init(struct pci_dev *dev, int pos)
    else
    iov->dev = dev;

    + mutex_init(&iov->reslock);
    dev->sriov = iov;
    dev->is_physfn = 1;
    rc = compute_max_vf_buses(dev);
    diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
    index a0941ade88eb..512d286ed8d6 100644
    --- a/drivers/pci/pci.h
    +++ b/drivers/pci/pci.h
    @@ -304,6 +304,19 @@ struct pci_sriov {
    u16 subsystem_device; /* VF subsystem device */
    resource_size_t barsz[PCI_SRIOV_NUM_BARS]; /* VF BAR size */
    bool drivers_autoprobe; /* Auto probing of VFs by driver */
    + /*
    + * reslock mutex is used for synchronizing updates to resources
    + * shared between PF and all associated VFs. For example, in
    + * SRIOV devices, PRI and PASID interfaces are shared between
    + * PF an all VFs, and hence we need proper locking mechanism to
    + * prevent both PF and VF update the PRI or PASID configuration
    + * registers at the same time.
    + * NOTE: Currently, this lock is shared by all capabilities that
    + * has shared resource between PF and VFs. If there is any performance
    + * impact then perhaps we need to create separate lock for each of
    + * the independent capability that has shared resources.
    + */
    + struct mutex reslock; /* PF/VF shared resource lock */
    };

    /**
    @@ -449,6 +462,27 @@ void pci_iov_update_resource(struct pci_dev *dev, int resno);
    resource_size_t pci_sriov_resource_alignment(struct pci_dev *dev, int resno);
    void pci_restore_iov_state(struct pci_dev *dev);
    int pci_iov_bus_range(struct pci_bus *bus);
    +static inline void pci_physfn_reslock(struct pci_dev *dev)
    +{
    + struct pci_dev *pf = pci_physfn(dev);
    +
    + /* For non SRIOV devices, locking is not needed */
    + if (!pf->is_physfn)
    + return;
    +
    + mutex_lock(&pf->sriov->reslock);
    +}
    +
    +static inline void pci_physfn_resunlock(struct pci_dev *dev)
    +{
    + struct pci_dev *pf = pci_physfn(dev);
    +
    + /* For non SRIOV devices, reslock is never held */
    + if (!pf->is_physfn)
    + return;
    +
    + mutex_unlock(&pf->sriov->reslock);
    +}

    #else
    static inline int pci_iov_init(struct pci_dev *dev)
    @@ -469,6 +503,12 @@ static inline int pci_iov_bus_range(struct pci_bus *bus)
    {
    return 0;
    }
    +static inline void pci_physfn_reslock(struct pci_dev *dev)
    +{
    +}
    +static inline void pci_physfn_resunlock(struct pci_dev *dev)
    +{
    +}

    #endif /* CONFIG_PCI_IOV */

    --
    2.21.0
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