Re: [PATCH v5 5/7] PCI/ATS: Add PASID support for PCIe VF devices

[Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>]

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.
> 
> 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.

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

> 
> >  	u16		pasid_cap;	/* PASID Capability offset */
> >  	u16		pasid_features;
> > +	atomic_t	pasid_ref_cnt;	/* Number of VFs with PASID enabled */
> >  #endif
> >  #ifdef CONFIG_PCI_P2PDMA
> >  	struct pci_p2pdma *p2pdma;
> > -- 
> > 2.21.0
> > 

-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer