linux-kernel - Re: [PATCH 3/4] iommu: Introduce device fault report API

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Date:   Fri, 31 May 2019 14:37:59 +0100
From:   Jean-Philippe Brucker <jean-philippe.brucker@....com>
To:     Robin Murphy <robin.murphy@....com>,
        "joro@...tes.org" <joro@...tes.org>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>
Cc:     "yi.l.liu@...ux.intel.com" <yi.l.liu@...ux.intel.com>,
        "ashok.raj@...el.com" <ashok.raj@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: Re: [PATCH 3/4] iommu: Introduce device fault report API

On 23/05/2019 19:56, Robin Murphy wrote:
> On 23/05/2019 19:06, Jean-Philippe Brucker wrote:
>> From: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>>
>> Traditionally, device specific faults are detected and handled within
>> their own device drivers. When IOMMU is enabled, faults such as DMA
>> related transactions are detected by IOMMU. There is no generic
>> reporting mechanism to report faults back to the in-kernel device
>> driver or the guest OS in case of assigned devices.
>>
>> This patch introduces a registration API for device specific fault
>> handlers. This differs from the existing iommu_set_fault_handler/
>> report_iommu_fault infrastructures in several ways:
>> - it allows to report more sophisticated fault events (both
>>    unrecoverable faults and page request faults) due to the nature
>>    of the iommu_fault struct
>> - it is device specific and not domain specific.
>>
>> The current iommu_report_device_fault() implementation only handles
>> the "shoot and forget" unrecoverable fault case. Handling of page
>> request faults or stalled faults will come later.
>>
>> Signed-off-by: Jacob Pan <jacob.jun.pan@...ux.intel.com>
>> Signed-off-by: Ashok Raj <ashok.raj@...el.com>
>> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@....com>
>> Signed-off-by: Eric Auger <eric.auger@...hat.com>
>> ---
>>   drivers/iommu/iommu.c | 127 ++++++++++++++++++++++++++++++++++++++++++
>>   include/linux/iommu.h |  29 ++++++++++
>>   2 files changed, 156 insertions(+)
>>
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index 67ee6623f9b2..d546f7baa0d4 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -644,6 +644,13 @@ int iommu_group_add_device(struct iommu_group *group, struct device *dev)
>>   		goto err_free_name;
>>   	}
>>   
>> +	dev->iommu_param = kzalloc(sizeof(*dev->iommu_param), GFP_KERNEL);
>> +	if (!dev->iommu_param) {
>> +		ret = -ENOMEM;
>> +		goto err_free_name;
>> +	}
>> +	mutex_init(&dev->iommu_param->lock);
>> +
> 
> Note that this gets a bit tricky when we come to move to move the 
> fwspec/ops/etc. into iommu_param, since that data can have a longer 
> lifespan than the group association. I'd suggest moving this management 
> out to the iommu_{probe,release}_device() level from the start, but 
> maybe we're happy to come back and change things later as necessary.

I'll do that, but iommu_probe_device() might still be too late.
According to of_iommu_configure() there might be cases where
iommu_probe_device() is called after iommu_fwspec_init(). So when moving
everything to iommu_param, we might need to introduce something like
iommu_get_dev_param() which allocates the param if it doesn't exist.

Thanks,
Jean