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charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, 31 Jul 2020 14:30:03 +0800 Lu Baolu wrote: > Hi Alex, > > On 2020/7/30 4:25, Alex Williamson wrote: > > On Tue, 14 Jul 2020 13:57:02 +0800 > > Lu Baolu 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 > >> Signed-off-by: Lu Baolu > >> --- > >> 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. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu