linux-kernel - Re: [PATCH v10 04/16] iommu: Cleanup iopf data structure definitions

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Message-ID: <cf1319f7-b91b-4161-8b62-2b0c03f53c16@linux.intel.com>
Date: Thu, 25 Jan 2024 19:33:45 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Joel Granados <j.granados@...sung.com>
Cc: baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
 Will Deacon <will@...nel.org>, Robin Murphy <robin.murphy@....com>,
 Jason Gunthorpe <jgg@...pe.ca>, Kevin Tian <kevin.tian@...el.com>,
 Jean-Philippe Brucker <jean-philippe@...aro.org>,
 Nicolin Chen <nicolinc@...dia.com>, Yi Liu <yi.l.liu@...el.com>,
 Jacob Pan <jacob.jun.pan@...ux.intel.com>,
 Longfang Liu <liulongfang@...wei.com>, Yan Zhao <yan.y.zhao@...el.com>,
 iommu@...ts.linux.dev, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
 Jason Gunthorpe <jgg@...dia.com>
Subject: Re: [PATCH v10 04/16] iommu: Cleanup iopf data structure definitions

On 2024/1/25 18:23, Joel Granados wrote:
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index e5b8b9110c13..24b5545352ae 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -56,7 +56,6 @@ static int iopf_complete_group(struct device *dev, struct iopf_fault *iopf,
>>   			       enum iommu_page_response_code status)
>>   {
>>   	struct iommu_page_response resp = {
>> -		.version		= IOMMU_PAGE_RESP_VERSION_1,
>>   		.pasid			= iopf->fault.prm.pasid,
>>   		.grpid			= iopf->fault.prm.grpid,
>>   		.code			= status,
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 68e648b55767..b88dc3e0595c 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -1494,10 +1494,6 @@ int iommu_page_response(struct device *dev,
>>   	if (!param || !param->fault_param)
>>   		return -EINVAL;
>>   
>> -	if (msg->version != IOMMU_PAGE_RESP_VERSION_1 ||
>> -	    msg->flags & ~IOMMU_PAGE_RESP_PASID_VALID)
>> -		return -EINVAL;
>> -
> I see that this function `iommu_page_response` eventually lands in
> drivers/iommu/io-pgfault.c as `iopf_group_response`. But it seems that
> the check for IOMMU_PAGE_RESP_PASID_VALID is dropped.
> 
> I see that after applying [1] and [2] there are only three places where
> IOMMU_PAGE_RESP_PASID_VALID appears in the code: One is the definition
> and the other two are just setting the value. We effectively dropped the

Yes, really. Thanks for pointing this out.

$ git grep IOMMU_PAGE_RESP_PASID_VALID
drivers/iommu/io-pgfault.c:             resp.flags = 
IOMMU_PAGE_RESP_PASID_VALID;
drivers/iommu/io-pgfault.c:                     resp.flags = 
IOMMU_PAGE_RESP_PASID_VALID;
include/linux/iommu.h:#define IOMMU_PAGE_RESP_PASID_VALID       (1 << 0)

> check. Is the drop intended? and if so, should we just get rid of
> IOMMU_PAGE_RESP_PASID_VALID?

In my opinion, we should keep this hardware detail in the individual
driver. When the page fault handling framework in IOMMU and IOMMUFD
subsystems includes a valid PASID in the fault message, the response
message should also contain the *same* PASID value. Individual drivers
should be responsible for deciding whether to include the PASID in the
messages they provide for the hardware.

> 
> Best
> 
> [1]https://lore.kernel.org/all/20240122054308.23901-1-baolu.lu@linux.intel.com
> [2]https://lore.kernel.org/all/20240122073903.24406-1-baolu.lu@linux.intel.com

Best regards,
baolu