Re: [PATCH v2 1/5] PCI/ATS: Add PRI support for PCIe VF devices

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

On 5/29/19 4:04 PM, Raj, Ashok wrote:
> 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@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;
> 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.

I am currently working on a fix to handle the bind issue (VF binding 
before PF). My next version will have this update.

But, regarding VF spec compliance checks, Is there any issue in having 
them in enable code ? Perhaps I can change dev_err to dev_warn and not 
return error if it found implementation errors. I found it useful to 
have them because it helped me in finding some faulty devices during my 
testing. Let me know your comments.

>
>
>>      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
>>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer