Re: [PATCH v5 2/7] PCI/ATS: Initialize PRI in pci_ats_init()

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

Hi,

Thanks for the review.

On 8/12/19 1:04 PM, Bjorn Helgaas wrote:
> On Thu, Aug 01, 2019 at 05:05:59PM -0700, sathyanarayanan.kuppuswamy@linux.intel.com wrote:
>> From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>>
>> Currently, PRI Capability checks are repeated across all PRI API's.
>> Instead, cache the capability check result in pci_pri_init() and use it
>> in other PRI API's. Also, since PRI is a shared resource between PF/VF,
>> initialize default values for common PRI features in pci_pri_init().
> This patch does two things, and it would be better if they were split:
>
>    1) Cache the PRI capability offset
>    2) Separate the PF and VF paths
Ok. I will split it into two patches in next version.
>
>> Signed-off-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
>> ---
>>   drivers/pci/ats.c       | 80 ++++++++++++++++++++++++++++-------------
>>   include/linux/pci-ats.h |  5 +++
>>   include/linux/pci.h     |  1 +
>>   3 files changed, 61 insertions(+), 25 deletions(-)
>>
>> diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
>> index cdd936d10f68..280be911f190 100644
>> --- a/drivers/pci/ats.c
>> +++ b/drivers/pci/ats.c
>> @@ -28,6 +28,8 @@ void pci_ats_init(struct pci_dev *dev)
>>   		return;
>>   
>>   	dev->ats_cap = pos;
>> +
>> +	pci_pri_init(dev);
>>   }
>>   
>>   /**
>> @@ -170,36 +172,72 @@ int pci_ats_page_aligned(struct pci_dev *pdev)
>>   EXPORT_SYMBOL_GPL(pci_ats_page_aligned);
>>   
>>   #ifdef CONFIG_PCI_PRI
>> +
>> +void pci_pri_init(struct pci_dev *pdev)
>> +{
>> +	u32 max_requests;
>> +	int pos;
>> +
>> +	/*
>> +	 * As per PCIe r4.0, sec 9.3.7.11, only PF is permitted to
>> +	 * implement PRI and all associated VFs can only use it.
>> +	 * Since PF already initialized the PRI parameters there is
>> +	 * no need to proceed further.
>> +	 */
>> +	if (pdev->is_virtfn)
>> +		return;
>> +
>> +	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> +	if (!pos)
>> +		return;
>> +
>> +	pci_read_config_dword(pdev, pos + PCI_PRI_MAX_REQ, &max_requests);
>> +
>> +	/*
>> +	 * Since PRI is a shared resource between PF and VF, we must not
>> +	 * configure Outstanding Page Allocation Quota as a per device
>> +	 * resource in pci_enable_pri(). So use maximum value possible
>> +	 * as default value.
>> +	 */
>> +	pci_write_config_dword(pdev, pos + PCI_PRI_ALLOC_REQ, max_requests);
>> +
>> +	pdev->pri_reqs_alloc = max_requests;
>> +	pdev->pri_cap = pos;
>> +}
>> +
>>   /**
>>    * pci_enable_pri - Enable PRI capability
>>    * @ pdev: PCI device structure
>>    *
>>    * Returns 0 on success, negative value on error
>> + *
>> + * TODO: Since PRI is a shared resource between PF/VF, don't update
>> + * Outstanding Page Allocation Quota in the same API as a per device
>> + * feature.
>>    */
>>   int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
>>   {
>>   	u16 control, status;
>>   	u32 max_requests;
>> -	int pos;
>>   
>>   	if (WARN_ON(pdev->pri_enabled))
>>   		return -EBUSY;
>>   
>> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> -	if (!pos)
>> +	if (!pdev->pri_cap)
>>   		return -EINVAL;
>>   
>> -	pci_read_config_word(pdev, pos + PCI_PRI_STATUS, &status);
>> +	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
>>   	if (!(status & PCI_PRI_STATUS_STOPPED))
>>   		return -EBUSY;
>>   
>> -	pci_read_config_dword(pdev, pos + PCI_PRI_MAX_REQ, &max_requests);
>> +	pci_read_config_dword(pdev, pdev->pri_cap + PCI_PRI_MAX_REQ,
>> +			      &max_requests);
>>   	reqs = min(max_requests, reqs);
>>   	pdev->pri_reqs_alloc = reqs;
>> -	pci_write_config_dword(pdev, pos + PCI_PRI_ALLOC_REQ, reqs);
>> +	pci_write_config_dword(pdev, pdev->pri_cap + PCI_PRI_ALLOC_REQ, reqs);
> The comment above says "don't update Outstanding Page Allocation
> Quota" but it looks like that's what this is doing.

I don't want to fix it in the current patch-set. It needs further 
scrutiny. That's why I have added the TODO comment for it.

Currently, intel-iommu and amd-iommu drivers (only users of 
pci_enable_pri()) hard-codes 32 as a default value for Outstanding Page 
Allocation Quota. Only exception is, amd-iommu sets this value as 1 for 
devices with erratum AMD_PRI_DEV_ERRATUM_LIMIT_REQ_ONE. There is no 
comment or spec reference that explains why 32 is chosen as default 
value. Also configuring 32 as per device max value will break for PF/VF 
devices since they share the PRI interface. So without clear history, I 
don't want to make any changes which might affect their functionality.

IMO, the correct way is to configure the Outstanding Page Allocation 
Quota with maximum value in pci_pri_init(). So, even if IOMMU can't 
handle more than 32 page request per device, it can fail properly and it 
should not affect the functionality.

I have added proper configuration for Outstanding Page Allocation Quota 
in pci_pri_init(), but it does not serve any purpose until we fix the 
part of the issue in pci_enable_pri(). If you want, I can remove it for 
now, and add it when fixing the issue in pci_enable_pri().
>
>>   	control = PCI_PRI_CTRL_ENABLE;
>> -	pci_write_config_word(pdev, pos + PCI_PRI_CTRL, control);
>> +	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
>>   
>>   	pdev->pri_enabled = 1;
>>   
>> @@ -216,18 +254,16 @@ EXPORT_SYMBOL_GPL(pci_enable_pri);
>>   void pci_disable_pri(struct pci_dev *pdev)
>>   {
>>   	u16 control;
>> -	int pos;
>>   
>>   	if (WARN_ON(!pdev->pri_enabled))
>>   		return;
>>   
>> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> -	if (!pos)
>> +	if (!pdev->pri_cap)
>>   		return;
>>   
>> -	pci_read_config_word(pdev, pos + PCI_PRI_CTRL, &control);
>> +	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, &control);
>>   	control &= ~PCI_PRI_CTRL_ENABLE;
>> -	pci_write_config_word(pdev, pos + PCI_PRI_CTRL, control);
>> +	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
>>   
>>   	pdev->pri_enabled = 0;
>>   }
>> @@ -241,17 +277,15 @@ void pci_restore_pri_state(struct pci_dev *pdev)
>>   {
>>   	u16 control = PCI_PRI_CTRL_ENABLE;
>>   	u32 reqs = pdev->pri_reqs_alloc;
>> -	int pos;
>>   
>>   	if (!pdev->pri_enabled)
>>   		return;
>>   
>> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> -	if (!pos)
>> +	if (!pdev->pri_cap)
>>   		return;
>>   
>> -	pci_write_config_dword(pdev, pos + PCI_PRI_ALLOC_REQ, reqs);
>> -	pci_write_config_word(pdev, pos + PCI_PRI_CTRL, control);
>> +	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);
>>   }
>>   EXPORT_SYMBOL_GPL(pci_restore_pri_state);
>>   
>> @@ -265,17 +299,15 @@ EXPORT_SYMBOL_GPL(pci_restore_pri_state);
>>   int pci_reset_pri(struct pci_dev *pdev)
>>   {
>>   	u16 control;
>> -	int pos;
>>   
>>   	if (WARN_ON(pdev->pri_enabled))
>>   		return -EBUSY;
>>   
>> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> -	if (!pos)
>> +	if (!pdev->pri_cap)
>>   		return -EINVAL;
>>   
>>   	control = PCI_PRI_CTRL_RESET;
>> -	pci_write_config_word(pdev, pos + PCI_PRI_CTRL, control);
>> +	pci_write_config_word(pdev, pdev->pri_cap + PCI_PRI_CTRL, control);
>>   
>>   	return 0;
>>   }
>> @@ -410,13 +442,11 @@ EXPORT_SYMBOL_GPL(pci_pasid_features);
>>   int pci_prg_resp_pasid_required(struct pci_dev *pdev)
>>   {
>>   	u16 status;
>> -	int pos;
>>   
>> -	pos = pci_find_ext_capability(pdev, PCI_EXT_CAP_ID_PRI);
>> -	if (!pos)
>> +	if (!pdev->pri_cap)
>>   		return 0;
>>   
>> -	pci_read_config_word(pdev, pos + PCI_PRI_STATUS, &status);
>> +	pci_read_config_word(pdev, pdev->pri_cap + PCI_PRI_STATUS, &status);
>>   
>>   	if (status & PCI_PRI_STATUS_PASID)
>>   		return 1;
>> diff --git a/include/linux/pci-ats.h b/include/linux/pci-ats.h
>> index 1a0bdaee2f32..33653d4ca94f 100644
>> --- a/include/linux/pci-ats.h
>> +++ b/include/linux/pci-ats.h
>> @@ -6,6 +6,7 @@
>>   
>>   #ifdef CONFIG_PCI_PRI
>>   
>> +void pci_pri_init(struct pci_dev *pdev);
> I think this could be moved to drivers/pci/pci.h, since it doesn't
> need to be visible outside drivers/pci/.
Makes sense. I will move it.
>
>>   int pci_enable_pri(struct pci_dev *pdev, u32 reqs);
>>   void pci_disable_pri(struct pci_dev *pdev);
>>   void pci_restore_pri_state(struct pci_dev *pdev);
>> @@ -13,6 +14,10 @@ int pci_reset_pri(struct pci_dev *pdev);
>>   
>>   #else /* CONFIG_PCI_PRI */
>>   
>> +static inline void pci_pri_init(struct pci_dev *pdev)
>> +{
>> +}
>> +
>>   static inline int pci_enable_pri(struct pci_dev *pdev, u32 reqs)
>>   {
>>   	return -ENODEV;
>> diff --git a/include/linux/pci.h b/include/linux/pci.h
>> index 9e700d9f9f28..56b55db099fc 100644
>> --- a/include/linux/pci.h
>> +++ b/include/linux/pci.h
>> @@ -455,6 +455,7 @@ struct pci_dev {
>>   	atomic_t	ats_ref_cnt;	/* Number of VFs with ATS enabled */
>>   #endif
>>   #ifdef CONFIG_PCI_PRI
>> +	u16		pri_cap;	/* PRI Capability offset */
>>   	u32		pri_reqs_alloc; /* Number of PRI requests allocated */
>>   #endif
>>   #ifdef CONFIG_PCI_PASID
>> -- 
>> 2.21.0
>>
-- 
Sathyanarayanan Kuppuswamy
Linux kernel developer