Re: [RFC v3 14/21] iommu: introduce device fault data

[Auger Eric <eric.auger@redhat.com>]

Hi Jean,

On 1/11/19 12:06 PM, Jean-Philippe Brucker wrote:
> On 10/01/2019 18:45, Jacob Pan wrote:
>> On Tue,  8 Jan 2019 11:26:26 +0100
>> Eric Auger <eric.auger@redhat.com> wrote:
>>
>>> From: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>>
>>> Device faults detected by IOMMU can be reported outside IOMMU
>>> subsystem for further processing. This patch intends to provide
>>> a generic device fault data such that device drivers can be
>>> communicated with IOMMU faults without model specific knowledge.
>>>
>>> The proposed format is the result of discussion at:
>>> https://lkml.org/lkml/2017/11/10/291
>>> Part of the code is based on Jean-Philippe Brucker's patchset
>>> (https://patchwork.kernel.org/patch/9989315/).
>>>
>>> The assumption is that model specific IOMMU driver can filter and
>>> handle most of the internal faults if the cause is within IOMMU driver
>>> control. Therefore, the fault reasons can be reported are grouped
>>> and generalized based common specifications such as PCI ATS.
>>>
>>> Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
>>> Signed-off-by: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
>>> Signed-off-by: Liu, Yi L <yi.l.liu@linux.intel.com>
>>> Signed-off-by: Ashok Raj <ashok.raj@intel.com>
>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>> [moved part of the iommu_fault_event struct in the uapi, enriched
>>>  the fault reasons to be able to map unrecoverable SMMUv3 errors]
>>> ---
>>>  include/linux/iommu.h      | 55 ++++++++++++++++++++++++-
>>>  include/uapi/linux/iommu.h | 83
>>> ++++++++++++++++++++++++++++++++++++++ 2 files changed, 136
>>> insertions(+), 2 deletions(-)
>>>
>>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>>> index 244c1a3d5989..1dedc2d247c2 100644
>>> --- a/include/linux/iommu.h
>>> +++ b/include/linux/iommu.h
>>> @@ -49,13 +49,17 @@ struct bus_type;
>>>  struct device;
>>>  struct iommu_domain;
>>>  struct notifier_block;
>>> +struct iommu_fault_event;
>>>  
>>>  /* iommu fault flags */
>>> -#define IOMMU_FAULT_READ	0x0
>>> -#define IOMMU_FAULT_WRITE	0x1
>>> +#define IOMMU_FAULT_READ		(1 << 0)
>>> +#define IOMMU_FAULT_WRITE		(1 << 1)
>>> +#define IOMMU_FAULT_EXEC		(1 << 2)
>>> +#define IOMMU_FAULT_PRIV		(1 << 3)
>>>  
>>>  typedef int (*iommu_fault_handler_t)(struct iommu_domain *,
>>>  			struct device *, unsigned long, int, void *);
>>> +typedef int (*iommu_dev_fault_handler_t)(struct iommu_fault_event *,
>>> void *); 
>>>  struct iommu_domain_geometry {
>>>  	dma_addr_t aperture_start; /* First address that can be
>>> mapped    */ @@ -255,6 +259,52 @@ struct iommu_device {
>>>  	struct device *dev;
>>>  };
>>>  
>>> +/**
>>> + * struct iommu_fault_event - Generic per device fault data
>>> + *
>>> + * - PCI and non-PCI devices
>>> + * - Recoverable faults (e.g. page request), information based on
>>> PCI ATS
>>> + * and PASID spec.
>>> + * - Un-recoverable faults of device interest
>>> + * - DMA remapping and IRQ remapping faults
>>> + *
>>> + * @fault: fault descriptor
>>> + * @device_private: if present, uniquely identify device-specific
>>> + *                  private data for an individual page request.
>>> + * @iommu_private: used by the IOMMU driver for storing
>>> fault-specific
>>> + *                 data. Users should not modify this field before
>>> + *                 sending the fault response.
>>> + */
>>> +struct iommu_fault_event {
>>> +	struct iommu_fault fault;
>>> +	u64 device_private;
>> I think we want to move device_private to uapi since it gets injected
>> into the guest, then returned by guest in case of page response. For
>> VT-d we also need 128 bits of private data. VT-d spec. 7.7.1
> 
> Ah, I didn't notice the format changed in VT-d rev3. On that topic, how
> do we manage future extensions to the iommu_fault struct? Should we add
> ~48 bytes of padding after device_private, along with some flags telling
> which field is valid, or deal with it using a structure version like we
> do for the invalidate and bind structs? In the first case, iommu_fault
> wouldn't fit in a 64-byte cacheline anymore, but I'm not sure we care.
> 
>> For exception tracking (e.g. unanswered page request), I can add timer
>> and list info later when I include PRQ. sounds ok?
>>> +	u64 iommu_private;
> [...]
>>> +/**
>>> + * struct iommu_fault - Generic fault data
>>> + *
>>> + * @type contains fault type
>>> + * @reason fault reasons if relevant outside IOMMU driver.
>>> + * IOMMU driver internal faults are not reported.
>>> + * @addr: tells the offending page address
>>> + * @fetch_addr: tells the address that caused an abort, if any
>>> + * @pasid: contains process address space ID, used in shared virtual
>>> memory
>>> + * @page_req_group_id: page request group index
>>> + * @last_req: last request in a page request group
>>> + * @pasid_valid: indicates if the PRQ has a valid PASID
>>> + * @prot: page access protection flag:
>>> + *	IOMMU_FAULT_READ, IOMMU_FAULT_WRITE
>>> + */
>>> +
>>> +struct iommu_fault {
>>> +	__u32	type;   /* enum iommu_fault_type */
>>> +	__u32	reason; /* enum iommu_fault_reason */
>>> +	__u64	addr;
>>> +	__u64	fetch_addr;
>>> +	__u32	pasid;
>>> +	__u32	page_req_group_id;
>>> +	__u32	last_req;
>>> +	__u32	pasid_valid;
>>> +	__u32	prot;
>>> +	__u32	access;
> 
> What does @access contain? Can it be squashed into @prot?
it was related to F_ACCESS event record and was a placeholder for
reporting access attributes of the input transaction (Rnw, InD, PnU
fields). But I wonder whether this is needed to implement such fine
level fault reporting. Do we really care?

Thanks

Eric
> 
> Thanks,
> Jean
> 
>> relocated to uapi, Yi can you confirm?
>> 	__u64 device_private[2];
>>
>>> +};
>>>  #endif /* _UAPI_IOMMU_H */
>>
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>