Re: [PATCH v2 2/5] iommu/vt-d: Allow SVA with device-specific IOPF

[Baolu Lu <baolu.lu@linux.intel.com>]

On 3/21/23 12:00 AM, Jacob Pan wrote:
> Hi BaoLu,

Hi Jacob,

> 
> On Thu,  9 Mar 2023 10:56:36 +0800, Lu Baolu<baolu.lu@linux.intel.com>
> wrote:
> 
>> Currently enabling SVA requires IOPF support from the IOMMU and device
>> PCI PRI. However, some devices can handle IOPF by itself without ever
>> sending PCI page requests nor advertising PRI capability.
>>
>> Allow SVA support with IOPF handled either by IOMMU (PCI PRI) or device
>> driver (device-specific IOPF). As long as IOPF could be handled, SVA
>> should continue to work.
>>
>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index 7c2f4bd33582..d2fcab9d8f61 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -4650,7 +4650,18 @@ static int intel_iommu_enable_sva(struct device
>> *dev) if (!(iommu->flags & VTD_FLAG_SVM_CAPABLE))
>>   		return -ENODEV;
>>   
>> -	if (!info->pasid_enabled || !info->pri_enabled ||
>> !info->ats_enabled)
>> +	if (!info->pasid_enabled)
>> +		return -EINVAL;
>> +
>> +	/*
>> +	 * Devices having device-specific I/O fault handling should not
>> +	 * support PCI/PRI.
>> +	 */
>> +	if (!info->pri_supported)
>> +		return 0;
> If you put this check at the very beginning, everything else should it be
> the same, right?

Even for device specific IOPF, PASID/ATS are still required on the IOMMU
side.

> 
> Still feel a little weird that, SVA is tied to PRI for PCI PRI but not for
> device specific IOPF.

PCI PRI and device specific IOPF *should* be equivalent. But the IOMMU
side has no means to check the capability of device-specific IOPF.
Therefore, IOMMU can only default that if the device driver enables SVA
on a non-PRI device, it will handle IOPF in its own way.

Best regards,
baolu