Messages in this thread | | | Subject | Re: [PATCH v3 3/4] iommu: Add iommu_aux_get_domain_for_dev() | From | Lu Baolu <> | Date | Mon, 3 Aug 2020 10:15:27 +0800 |
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Hi Alex,
On 8/1/20 2:14 AM, Alex Williamson wrote: > On Fri, 31 Jul 2020 14:30:03 +0800 > Lu Baolu <baolu.lu@linux.intel.com> wrote: > >> Hi Alex, >> >> On 2020/7/30 4:25, Alex Williamson wrote: >>> On Tue, 14 Jul 2020 13:57:02 +0800 >>> Lu Baolu<baolu.lu@linux.intel.com> wrote: >>> >>>> The device driver needs an API to get its aux-domain. A typical usage >>>> scenario is: >>>> >>>> unsigned long pasid; >>>> struct iommu_domain *domain; >>>> struct device *dev = mdev_dev(mdev); >>>> struct device *iommu_device = vfio_mdev_get_iommu_device(dev); >>>> >>>> domain = iommu_aux_get_domain_for_dev(dev); >>>> if (!domain) >>>> return -ENODEV; >>>> >>>> pasid = iommu_aux_get_pasid(domain, iommu_device); >>>> if (pasid <= 0) >>>> return -EINVAL; >>>> >>>> /* Program the device context */ >>>> .... >>>> >>>> This adds an API for such use case. >>>> >>>> Suggested-by: Alex Williamson<alex.williamson@redhat.com> >>>> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com> >>>> --- >>>> drivers/iommu/iommu.c | 18 ++++++++++++++++++ >>>> include/linux/iommu.h | 7 +++++++ >>>> 2 files changed, 25 insertions(+) >>>> >>>> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c >>>> index cad5a19ebf22..434bf42b6b9b 100644 >>>> --- a/drivers/iommu/iommu.c >>>> +++ b/drivers/iommu/iommu.c >>>> @@ -2817,6 +2817,24 @@ void iommu_aux_detach_group(struct iommu_domain *domain, >>>> } >>>> EXPORT_SYMBOL_GPL(iommu_aux_detach_group); >>>> >>>> +struct iommu_domain *iommu_aux_get_domain_for_dev(struct device *dev) >>>> +{ >>>> + struct iommu_domain *domain = NULL; >>>> + struct iommu_group *group; >>>> + >>>> + group = iommu_group_get(dev); >>>> + if (!group) >>>> + return NULL; >>>> + >>>> + if (group->aux_domain_attached) >>>> + domain = group->domain; >>> Why wouldn't the aux domain flag be on the domain itself rather than >>> the group? Then if we wanted sanity checking in patch 1/ we'd only >>> need to test the flag on the object we're provided. >> >> Agreed. Given that a group may contain both non-aux and aux devices, >> adding such flag in iommu_group doesn't make sense. >> >>> >>> If we had such a flag, we could create an iommu_domain_is_aux() >>> function and then simply use iommu_get_domain_for_dev() and test that >>> it's an aux domain in the example use case. It seems like that would >>> resolve the jump from a domain to an aux-domain just as well as adding >>> this separate iommu_aux_get_domain_for_dev() interface. The is_aux >>> test might also be useful in other cases too. >> >> Let's rehearsal our use case. >> >> unsigned long pasid; >> struct iommu_domain *domain; >> struct device *dev = mdev_dev(mdev); >> struct device *iommu_device = vfio_mdev_get_iommu_device(dev); >> >> [1] domain = iommu_get_domain_for_dev(dev); >> if (!domain) >> return -ENODEV; >> >> [2] pasid = iommu_aux_get_pasid(domain, iommu_device); >> if (pasid <= 0) >> return -EINVAL; >> >> /* Program the device context */ >> .... >> >> The reason why I add this iommu_aux_get_domain_for_dev() is that we need >> to make sure the domain got at [1] is valid to be used at [2]. >> >> https://lore.kernel.org/linux-iommu/20200707150408.474d81f1@x1.home/ > > Yep, I thought that was a bit of a leap in logic. > >> When calling into iommu_aux_get_pasid(), the iommu driver should make >> sure that @domain is a valid aux-domain for @iommu_device. Hence, for >> our use case, it seems that there's no need for a is_aux_domain() api. >> >> Anyway, I'm not against adding a new is_aux_domain() api if there's a >> need elsewhere. > > I think it could work either way, we could have an > iommu_get_aux_domain_for_dev() which returns NULL if the domain is not > an aux domain, or we could use iommu_get_domain_for_dev() and the > caller could test the domain with iommu_is_aux_domain() if they need to > confirm if it's an aux domain. The former could even be written using > the latter, a wrapper of iommu_get_domain_for_dev() that checks aux > property before returning.
Okay. So iommu_get_domain_for_dev() and iommu_is_aux_domain() are what we wanted. The iommu_get_domain_for_dev() could be a simple wrapper of them.
Thanks a lot for the guide. I will implement a new version according to the feedbacks.
Best regards, baolu
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