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

Auger Eric
2019-01-15T21:27:11Z

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 */
>>
>> _______________________________________________
>> iommu mailing list
>> iommu@lists.linux-foundation.org
>> https://lists.linuxfoundation.org/mailman/listinfo/iommu
>>
>