Re: [PATCH v3 1/8] iommu: Add ops entry for supported default domain type

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Robin,

On 5/7/19 6:28 PM, Robin Murphy wrote:
> On 06/05/2019 16:32, Tom Murphy via iommu wrote:
>> The AMD driver already solves this problem and uses the generic
>> iommu_request_dm_for_dev function. It seems like both drivers have the
>> same problem and could use the same solution. Is there any reason we
>> can't have use the same solution for the intel and amd driver?
>>
>> Could we just  copy the implementation of the AMD driver? It would be
>> nice to have the same behavior across both drivers especially as we
>> move to make both drivers use more generic code.
> 
> TBH I don't think the API really needs to be involved at all here. 
> Drivers can already not provide the requested default domain type if 
> they don't support it, so as long as the driver can ensure that the 
> device ends up with IOMMU or direct DMA ops as appropriate, I don't see 
> any great problem with drivers just returning a passthrough domain when 
> a DMA domain was requested, or vice versa (and logging a message that 
> the requested type was overridden). The only type that we really do have 
> to honour strictly is non-default (i.e. unmanaged) domains.

I agree with you that we only have to honor strictly the non-default
domains. But domain type saved in iommu_domain is consumed in iommu.c
and exposed to user through sysfs. It's not clean if the iommu driver
silently replace the default domain.

Best regards,
Lu Baolu

> 
> Robin.
> 
>> On Mon, Apr 29, 2019 at 3:16 AM Lu Baolu <baolu.lu@linux.intel.com> 
>> wrote:
>>>
>>> This adds an optional ops entry to query the default domain
>>> types supported by the iommu driver for  a specific device.
>>> This is necessary in cases where the iommu driver can only
>>> support a specific type of default domain for a device. In
>>> normal cases, this ops will return IOMMU_DOMAIN_ANY which
>>> indicates that the iommu driver supports both IOMMU_DOMAIN_DMA
>>> and IOMMU_DOMAIN_IDENTITY, hence the static default domain
>>> type will be used.
>>>
>>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>>> ---
>>>   drivers/iommu/iommu.c | 13 ++++++++++---
>>>   include/linux/iommu.h | 11 +++++++++++
>>>   2 files changed, 21 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
>>> index acd6830e6e9b..1ad9a1f2e078 100644
>>> --- a/drivers/iommu/iommu.c
>>> +++ b/drivers/iommu/iommu.c
>>> @@ -1097,15 +1097,22 @@ struct iommu_group 
>>> *iommu_group_get_for_dev(struct device *dev)
>>>           * IOMMU driver.
>>>           */
>>>          if (!group->default_domain) {
>>> +               unsigned int domain_type = IOMMU_DOMAIN_ANY;
>>>                  struct iommu_domain *dom;
>>>
>>> -               dom = __iommu_domain_alloc(dev->bus, 
>>> iommu_def_domain_type);
>>> -               if (!dom && iommu_def_domain_type != IOMMU_DOMAIN_DMA) {
>>> +               if (ops->def_domain_type)
>>> +                       domain_type = ops->def_domain_type(dev);
>>> +
>>> +               if (domain_type == IOMMU_DOMAIN_ANY)
>>> +                       domain_type = iommu_def_domain_type;
>>> +
>>> +               dom = __iommu_domain_alloc(dev->bus, domain_type);
>>> +               if (!dom && domain_type != IOMMU_DOMAIN_DMA) {
>>>                          dom = __iommu_domain_alloc(dev->bus, 
>>> IOMMU_DOMAIN_DMA);
>>>                          if (dom) {
>>>                                  dev_warn(dev,
>>>                                           "failed to allocate default 
>>> IOMMU domain of type %u; falling back to IOMMU_DOMAIN_DMA",
>>> -                                        iommu_def_domain_type);
>>> +                                        domain_type);
>>>                          }
>>>                  }
>>>
>>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>>> index 8239ece9fdfc..ba9a5b996a63 100644
>>> --- a/include/linux/iommu.h
>>> +++ b/include/linux/iommu.h
>>> @@ -79,12 +79,16 @@ struct iommu_domain_geometry {
>>>    *     IOMMU_DOMAIN_DMA        - Internally used for DMA-API 
>>> implementations.
>>>    *                               This flag allows IOMMU drivers to 
>>> implement
>>>    *                               certain optimizations for these 
>>> domains
>>> + *     IOMMU_DOMAIN_ANY        - All domain types defined here
>>>    */
>>>   #define IOMMU_DOMAIN_BLOCKED   (0U)
>>>   #define IOMMU_DOMAIN_IDENTITY  (__IOMMU_DOMAIN_PT)
>>>   #define IOMMU_DOMAIN_UNMANAGED (__IOMMU_DOMAIN_PAGING)
>>>   #define IOMMU_DOMAIN_DMA       (__IOMMU_DOMAIN_PAGING |        \
>>>                                   __IOMMU_DOMAIN_DMA_API)
>>> +#define IOMMU_DOMAIN_ANY       (IOMMU_DOMAIN_IDENTITY |        \
>>> +                                IOMMU_DOMAIN_UNMANAGED |       \
>>> +                                IOMMU_DOMAIN_DMA)
>>>
>>>   struct iommu_domain {
>>>          unsigned type;
>>> @@ -196,6 +200,11 @@ enum iommu_dev_features {
>>>    * @dev_feat_enabled: check enabled feature
>>>    * @aux_attach/detach_dev: aux-domain specific attach/detach entries.
>>>    * @aux_get_pasid: get the pasid given an aux-domain
>>> + * @def_domain_type: get per-device default domain type that the IOMMU
>>> + *             driver is able to support. Valid returns values:
>>> + *             - IOMMU_DOMAIN_DMA: only suports non-identity domain
>>> + *             - IOMMU_DOMAIN_IDENTITY: only supports identity domain
>>> + *             - IOMMU_DOMAIN_ANY: supports all
>>>    * @pgsize_bitmap: bitmap of all possible supported page sizes
>>>    */
>>>   struct iommu_ops {
>>> @@ -251,6 +260,8 @@ struct iommu_ops {
>>>          void (*aux_detach_dev)(struct iommu_domain *domain, struct 
>>> device *dev);
>>>          int (*aux_get_pasid)(struct iommu_domain *domain, struct 
>>> device *dev);
>>>
>>> +       int (*def_domain_type)(struct device *dev);
>>> +
>>>          unsigned long pgsize_bitmap;
>>>   };
>>>
>>> -- 
>>> 2.17.1
>>>
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>