Re: [PATCH 3/3] iommu: Convert response code from failure to invalid

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

On 7/10/24 5:56 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Wednesday, July 10, 2024 4:34 PM
>>
>> In the iopf deliver path, iommu_report_device_fault() currently responds
>> a code of "Response Failure" to the hardware if it can't find a suitable
>> iopf-capable domain where the page faults should be handled. The Response
>> Failure is defined in PCI spec (section 10.4.2.1) as a catastrophic error,
>> and the device will disable PRI for the function.
>>
>> Failing to dispatch a set of fault messages is not a catastrophic error
>> and the iommu core has no code to recover the PRI once it is disabled.
>>
>> Replace it with a response code of "Invalid Response".
>>
>> Fixes: b554e396e51c ("iommu: Make iopf_group_response() return void")
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/io-pgfault.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index cd679c13752e..b8270ee5dcdb 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -229,7 +229,7 @@ void iommu_report_device_fault(struct device *dev,
>> struct iopf_fault *evt)
>>   err_abort:
>>   	dev_warn_ratelimited(dev, "iopf with pasid %d aborted\n",
>>   			     fault->prm.pasid);
>> -	iopf_group_response(group, IOMMU_PAGE_RESP_FAILURE);
>> +	iopf_group_response(group, IOMMU_PAGE_RESP_INVALID);
>>   	if (group == &abort_group)
>>   		__iopf_free_group(group);
>>   	else
> 
> this doesn't match the spec words on the use of INVALID:
> 
>    One or more pages within the associated PRG do not exist or
>    requests access privilege(s) that cannot be granted. Unless the
>    page mapping associated with the Function is altered, re-issuance
>    of the associated request will never result in success.
> 
> this situation is not related to the permission of page mapping. Instead
> it's a global problem applying to all functions submitting page requests
> at this moment.
> 
> Though using FAILURE affects more functions sharing the PRI interface,
> it also proactively avoids adding more in-fly requests to worsen the
> low memory situation.
> 
> So none of the options looks perfect to me, but the existing code
> responding FAILURE is more aligned to the spec?

Fair enough. Perhaps we can keep the existing code as-is unless any real
issues arise.

Thanks,
baolu