Re: [RFC PATCH v2 1/6] iommu: Evolve to support more scenarios of using IOPF

[Shenming Lu <lushenming@huawei.com>]

Hi Baolu,

On 2021/3/10 10:09, Lu Baolu wrote:
> Hi Shenming,
> 
> On 3/9/21 2:22 PM, Shenming Lu wrote:
>> This patch follows the discussion here:
>>
>> https://lore.kernel.org/linux-acpi/YAaxjmJW+ZMvrhac@myrica/
>>
>> In order to support more scenarios of using IOPF (mainly consider
>> the nested extension), besides keeping IOMMU_DEV_FEAT_IOPF as a
>> general capability for whether delivering faults through the IOMMU,
>> we extend iommu_register_fault_handler() with flags and introduce
>> IOPF_REPORT_FLAT and IOPF_REPORT_NESTED to describe the page fault
>> reporting capability under a specific configuration.
>> IOPF_REPORT_NESTED needs additional info to indicate which level/stage
>> is concerned since the fault client may be interested in only one
>> level.
>>
>> Signed-off-by: Shenming Lu <lushenming@huawei.com>
>> ---
>>   .../iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c   |  3 +-
>>   drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c   | 11 ++--
>>   drivers/iommu/io-pgfault.c                    |  4 --
>>   drivers/iommu/iommu.c                         | 56 ++++++++++++++++++-
>>   include/linux/iommu.h                         | 21 ++++++-
>>   include/uapi/linux/iommu.h                    |  3 +
>>   6 files changed, 85 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
>> index ee66d1f4cb81..5de9432349d4 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
>> @@ -482,7 +482,8 @@ static int arm_smmu_master_sva_enable_iopf(struct arm_smmu_master *master)
>>       if (ret)
>>           return ret;
>>   -    ret = iommu_register_device_fault_handler(dev, iommu_queue_iopf, dev);
>> +    ret = iommu_register_device_fault_handler(dev, iommu_queue_iopf,
>> +                          IOPF_REPORT_FLAT, dev);
>>       if (ret) {
>>           iopf_queue_remove_device(master->smmu->evtq.iopf, dev);
>>           return ret;
>> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> index 363744df8d51..f40529d0075d 100644
>> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
>> @@ -1447,10 +1447,6 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
>>           return -EOPNOTSUPP;
>>       }
>>   -    /* Stage-2 is always pinned at the moment */
>> -    if (evt[1] & EVTQ_1_S2)
>> -        return -EFAULT;
>> -
>>       if (evt[1] & EVTQ_1_RnW)
>>           perm |= IOMMU_FAULT_PERM_READ;
>>       else
>> @@ -1468,13 +1464,18 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
>>               .flags = IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE,
>>               .grpid = FIELD_GET(EVTQ_1_STAG, evt[1]),
>>               .perm = perm,
>> -            .addr = FIELD_GET(EVTQ_2_ADDR, evt[2]),
>>           };
>>             if (ssid_valid) {
>>               flt->prm.flags |= IOMMU_FAULT_PAGE_REQUEST_PASID_VALID;
>>               flt->prm.pasid = FIELD_GET(EVTQ_0_SSID, evt[0]);
>>           }
>> +
>> +        if (evt[1] & EVTQ_1_S2) {
>> +            flt->prm.flags |= IOMMU_FAULT_PAGE_REQUEST_L2;
>> +            flt->prm.addr = FIELD_GET(EVTQ_3_IPA, evt[3]);
>> +        } else
>> +            flt->prm.addr = FIELD_GET(EVTQ_2_ADDR, evt[2]);
>>       } else {
>>           flt->type = IOMMU_FAULT_DMA_UNRECOV;
>>           flt->event = (struct iommu_fault_unrecoverable) {
>> diff --git a/drivers/iommu/io-pgfault.c b/drivers/iommu/io-pgfault.c
>> index 1df8c1dcae77..abf16e06bcf5 100644
>> --- a/drivers/iommu/io-pgfault.c
>> +++ b/drivers/iommu/io-pgfault.c
>> @@ -195,10 +195,6 @@ int iommu_queue_iopf(struct iommu_fault *fault, void *cookie)
>>         lockdep_assert_held(&param->lock);
>>   -    if (fault->type != IOMMU_FAULT_PAGE_REQ)
>> -        /* Not a recoverable page fault */
>> -        return -EOPNOTSUPP;
>> -
> 
> Any reasons why do you want to remove this check?

My thought was to make the reporting cap more detailed: IOPF_REPORT_ is only for recoverable
page faults (IOMMU_FAULT_PAGE_REQ), and we may add UNRECOV_FAULT_REPORT_ later for unrecoverable
faults (IOMMU_FAULT_DMA_UNRECOV)...

> 
>>       /*
>>        * As long as we're holding param->lock, the queue can't be unlinked
>>        * from the device and therefore cannot disappear.
>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>> index d0b0a15dba84..cb1d93b00f7d 100644
>> --- a/drivers/iommu/iommu.c
>> +++ b/drivers/iommu/iommu.c
>> @@ -1056,6 +1056,40 @@ int iommu_group_unregister_notifier(struct iommu_group *group,
>>   }
>>   EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
>>   +/*
>> + * iommu_update_device_fault_handler - Update the device fault handler via flags
>> + * @dev: the device
>> + * @mask: bits(not set) to clear
>> + * @set: bits to set
>> + *
>> + * Update the device fault handler installed by
>> + * iommu_register_device_fault_handler().
>> + *
>> + * Return 0 on success, or an error.
>> + */
>> +int iommu_update_device_fault_handler(struct device *dev, u32 mask, u32 set)
>> +{
>> +    struct dev_iommu *param = dev->iommu;
>> +    int ret = 0;
>> +
>> +    if (!param)
>> +        return -EINVAL;
>> +
>> +    mutex_lock(&param->lock);
>> +
>> +    if (param->fault_param) {
>> +        ret = -EINVAL;
>> +        goto out_unlock;
>> +    }
>> +
>> +    param->fault_param->flags = (param->fault_param->flags & mask) | set;
>> +
>> +out_unlock:
>> +    mutex_unlock(&param->lock);
>> +    return ret;
>> +}
>> +EXPORT_SYMBOL_GPL(iommu_update_device_fault_handler);
> 
> When and why will this API be used? Why not registering the fault
> handling capabilities of a device driver only once during probe()?

In VFIO, stage 2 IOPF might be enabled via an ioctl from the userspace (in this series),
while stage 1 IOPF is enabled from vfio_pci_enable() [1] for nested mode, they are
configured separately, and currently each device can only have one iommu dev fault
handler. So I choose to add a update interface for the second one.

[1] https://patchwork.kernel.org/project/kvm/patch/20210223210625.604517-6-eric.auger@redhat.com/

> 
>> +
>>   /**
>>    * iommu_register_device_fault_handler() - Register a device fault handler
>>    * @dev: the device
>> @@ -1076,11 +1110,14 @@ EXPORT_SYMBOL_GPL(iommu_group_unregister_notifier);
>>    */
>>   int iommu_register_device_fault_handler(struct device *dev,
>>                       iommu_dev_fault_handler_t handler,
>> -                    void *data)
>> +                    u32 flags, void *data)
>>   {
>>       struct dev_iommu *param = dev->iommu;
>>       int ret = 0;
>>   +    if (flags & IOPF_REPORT_FLAT && flags & IOPF_REPORT_NESTED)
>> +        return -EINVAL;
>> +
>>       if (!param)
>>           return -EINVAL;
>>   @@ -1099,6 +1136,7 @@ int iommu_register_device_fault_handler(struct device *dev,
>>           goto done_unlock;
>>       }
>>       param->fault_param->handler = handler;
>> +    param->fault_param->flags = flags;
>>       param->fault_param->data = data;
>>       mutex_init(&param->fault_param->lock);
>>       INIT_LIST_HEAD(&param->fault_param->faults);
>> @@ -1177,6 +1215,22 @@ int iommu_report_device_fault(struct device *dev, struct iommu_fault_event *evt)
>>           goto done_unlock;
>>       }
>>   +    /* The unrecoverable fault reporting is not supported at the moment. */
>> +    if (evt->fault.type != IOMMU_FAULT_PAGE_REQ)
>> +        return -EOPNOTSUPP;
> 
> Any reasons why do you want to disable reporting an unrecoverable fault?

When I add UNRECOV_FAULT_REPORT_ (mentioned above), I will enable the unrecoverable fault
reporting if the fault client concerns it. Sorry for this. :-)

> 
>> +
>> +    if (evt->fault.type == IOMMU_FAULT_PAGE_REQ) {
>> +        if (fparam->flags & IOPF_REPORT_NESTED) {
>> +            if (evt->fault.prm.flags & IOMMU_FAULT_PAGE_REQUEST_L2 &&
>> +                !(fparam->flags & IOPF_REPORT_NESTED_L2_CONCERNED))
>> +                return -EOPNOTSUPP;
>> +            if (!(evt->fault.prm.flags & IOMMU_FAULT_PAGE_REQUEST_L2) &&
>> +                !(fparam->flags & IOPF_REPORT_NESTED_L1_CONCERNED))
>> +                return -EOPNOTSUPP;
>> +        } else if (!(fparam->flags & IOPF_REPORT_FLAT))
>> +            return -EOPNOTSUPP;
>> +    }
>> +
>>       if (evt->fault.type == IOMMU_FAULT_PAGE_REQ &&
>>           (evt->fault.prm.flags & IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE)) {
>>           evt_pending = kmemdup(evt, sizeof(struct iommu_fault_event),
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 86d688c4418f..f03d761e8310 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -352,12 +352,21 @@ struct iommu_fault_event {
>>   /**
>>    * struct iommu_fault_param - per-device IOMMU fault data
>>    * @handler: Callback function to handle IOMMU faults at device level
>> + * @flags: Indicates whether the fault reporting is available under a
>> + *       specific configuration (1st/2nd-level-only(FLAT), or nested).
>> + *       IOPF_REPORT_NESTED needs to additionally know which level/stage
>> + *       is concerned.
> 
> If IOPF_REPORT_NESTED only is not valid why do you want to define it?

Yeah, it seems that IOPF_REPORT_NESTED is unnecessary, IOPF_REPORT_NESTED_L1 + IOPF_REPORT_NESTED_L2
is enough...

Thanks for your comments!
Shenming

> 
>>    * @data: handler private data
>>    * @faults: holds the pending faults which needs response
>>    * @lock: protect pending faults list
>>    */
>>   struct iommu_fault_param {
>>       iommu_dev_fault_handler_t handler;
>> +#define IOPF_REPORT_FLAT            (1 << 0)
>> +#define IOPF_REPORT_NESTED            (1 << 1)
>> +#define IOPF_REPORT_NESTED_L1_CONCERNED        (1 << 2)
>> +#define IOPF_REPORT_NESTED_L2_CONCERNED        (1 << 3)
>> +    u32 flags;
>>       void *data;
>>       struct list_head faults;
>>       struct mutex lock;
>> @@ -509,9 +518,11 @@ extern int iommu_group_register_notifier(struct iommu_group *group,
>>                        struct notifier_block *nb);
>>   extern int iommu_group_unregister_notifier(struct iommu_group *group,
>>                          struct notifier_block *nb);
>> +extern int iommu_update_device_fault_handler(struct device *dev,
>> +                         u32 mask, u32 set);
>>   extern int iommu_register_device_fault_handler(struct device *dev,
>>                       iommu_dev_fault_handler_t handler,
>> -                    void *data);
>> +                    u32 flags, void *data);
>>     extern int iommu_unregister_device_fault_handler(struct device *dev);
>>   @@ -873,10 +884,16 @@ static inline int iommu_group_unregister_notifier(struct iommu_group *group,
>>       return 0;
>>   }
>>   +static inline int iommu_update_device_fault_handler(struct device *dev,
>> +                            u32 mask, u32 set)
>> +{
>> +    return -ENODEV;
>> +}
>> +
>>   static inline
>>   int iommu_register_device_fault_handler(struct device *dev,
>>                       iommu_dev_fault_handler_t handler,
>> -                    void *data)
>> +                    u32 flags, void *data)
>>   {
>>       return -ENODEV;
>>   }
>> diff --git a/include/uapi/linux/iommu.h b/include/uapi/linux/iommu.h
>> index e1d9e75f2c94..0ce0dfb7713e 100644
>> --- a/include/uapi/linux/iommu.h
>> +++ b/include/uapi/linux/iommu.h
>> @@ -85,6 +85,8 @@ struct iommu_fault_unrecoverable {
>>    *         When IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID is set, the page response
>>    *         must have the same PASID value as the page request. When it is clear,
>>    *         the page response should not have a PASID.
>> + *         If IOMMU_FAULT_PAGE_REQUEST_L2 is set, the fault occurred at the
>> + *         second level/stage, otherwise, occurred at the first level.
>>    * @pasid: Process Address Space ID
>>    * @grpid: Page Request Group Index
>>    * @perm: requested page permissions (IOMMU_FAULT_PERM_* values)
>> @@ -96,6 +98,7 @@ struct iommu_fault_page_request {
>>   #define IOMMU_FAULT_PAGE_REQUEST_LAST_PAGE    (1 << 1)
>>   #define IOMMU_FAULT_PAGE_REQUEST_PRIV_DATA    (1 << 2)
>>   #define IOMMU_FAULT_PAGE_RESPONSE_NEEDS_PASID    (1 << 3)
>> +#define IOMMU_FAULT_PAGE_REQUEST_L2        (1 << 4)
>>       __u32    flags;
>>       __u32    pasid;
>>       __u32    grpid;
>>
> 
> Best regards,
> baolu
> .