Messages in this thread Patch in this message | | | Date | Tue, 21 Dec 2021 16:50:56 +0000 | Subject | Re: [PATCH v4 07/13] iommu: Add iommu_at[de]tach_device_shared() for multi-device groups | From | Robin Murphy <> |
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On 2021-12-17 06:37, Lu Baolu wrote: > The iommu_attach/detach_device() interfaces were exposed for the device > drivers to attach/detach their own domains. The commit <426a273834eae> > ("iommu: Limit iommu_attach/detach_device to device with their own group") > restricted them to singleton groups to avoid different device in a group > attaching different domain. > > As we've introduced device DMA ownership into the iommu core. We can now > introduce interfaces for muliple-device groups, and "all devices are in the > same address space" is still guaranteed. > > The iommu_attach/detach_device_shared() could be used when multiple drivers > sharing the group claim the DMA_OWNER_PRIVATE_DOMAIN ownership. The first > call of iommu_attach_device_shared() attaches the domain to the group. > Other drivers could join it later. The domain will be detached from the > group after all drivers unjoin it.
I don't see the point of this at all - if you really want to hide the concept of IOMMU groups away from drivers then just make iommu_{attach,detach}_device() do the right thing. At least the iommu_group_get_for_dev() plus iommu_{attach,detach}_group() API is clear - this proposal is the worst of both worlds, in that drivers still have to be just as aware of groups in order to know whether to call the _shared interface or not, except it's now entirely implicit and non-obvious.
Otherwise just add the housekeeping stuff to iommu_{attach,detach}_group() - there's no way we want *three* attach/detach interfaces all with different semantics.
It's worth taking a step back and realising that overall, this is really just a more generalised and finer-grained extension of what 426a273834ea already did for non-group-aware code, so it makes little sense *not* to integrate it into the existing interfaces.
Robin.
> Signed-off-by: Jason Gunthorpe <jgg@nvidia.com> > Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com> > Tested-by: Dmitry Osipenko <digetx@gmail.com> > --- > include/linux/iommu.h | 13 +++++++ > drivers/iommu/iommu.c | 79 +++++++++++++++++++++++++++++++++++++++++++ > 2 files changed, 92 insertions(+) > > diff --git a/include/linux/iommu.h b/include/linux/iommu.h > index 5ad4cf13370d..1bc03118dfb3 100644 > --- a/include/linux/iommu.h > +++ b/include/linux/iommu.h > @@ -703,6 +703,8 @@ int iommu_group_set_dma_owner(struct iommu_group *group, enum iommu_dma_owner ow > void *owner_cookie); > void iommu_group_release_dma_owner(struct iommu_group *group, enum iommu_dma_owner owner); > bool iommu_group_dma_owner_unclaimed(struct iommu_group *group); > +int iommu_attach_device_shared(struct iommu_domain *domain, struct device *dev); > +void iommu_detach_device_shared(struct iommu_domain *domain, struct device *dev); > > #else /* CONFIG_IOMMU_API */ > > @@ -743,11 +745,22 @@ static inline int iommu_attach_device(struct iommu_domain *domain, > return -ENODEV; > } > > +static inline int iommu_attach_device_shared(struct iommu_domain *domain, > + struct device *dev) > +{ > + return -ENODEV; > +} > + > static inline void iommu_detach_device(struct iommu_domain *domain, > struct device *dev) > { > } > > +static inline void iommu_detach_device_shared(struct iommu_domain *domain, > + struct device *dev) > +{ > +} > + > static inline struct iommu_domain *iommu_get_domain_for_dev(struct device *dev) > { > return NULL; > diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c > index 8bec71b1cc18..3ad66cb9bedc 100644 > --- a/drivers/iommu/iommu.c > +++ b/drivers/iommu/iommu.c > @@ -50,6 +50,7 @@ struct iommu_group { > struct list_head entry; > enum iommu_dma_owner dma_owner; > unsigned int owner_cnt; > + unsigned int attach_cnt; > void *owner_cookie; > }; > > @@ -3512,3 +3513,81 @@ void iommu_device_release_dma_owner(struct device *dev, enum iommu_dma_owner own > iommu_group_put(group); > } > EXPORT_SYMBOL_GPL(iommu_device_release_dma_owner); > + > +/** > + * iommu_attach_device_shared() - Attach shared domain to a device > + * @domain: The shared domain. > + * @dev: The device. > + * > + * Similar to iommu_attach_device(), but allowed for shared-group devices > + * and guarantees that all devices in an iommu group could only be attached > + * by a same iommu domain. The caller should explicitly set the dma ownership > + * of DMA_OWNER_PRIVATE_DOMAIN or DMA_OWNER_PRIVATE_DOMAIN_USER type before > + * calling it and use the paired helper iommu_detach_device_shared() for > + * cleanup. > + */ > +int iommu_attach_device_shared(struct iommu_domain *domain, struct device *dev) > +{ > + struct iommu_group *group; > + int ret = 0; > + > + group = iommu_group_get(dev); > + if (!group) > + return -ENODEV; > + > + mutex_lock(&group->mutex); > + if (group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN && > + group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN_USER) { > + ret = -EPERM; > + goto unlock_out; > + } > + > + if (group->attach_cnt) { > + if (group->domain != domain) { > + ret = -EBUSY; > + goto unlock_out; > + } > + } else { > + ret = __iommu_attach_group(domain, group); > + if (ret) > + goto unlock_out; > + } > + > + group->attach_cnt++; > +unlock_out: > + mutex_unlock(&group->mutex); > + iommu_group_put(group); > + > + return ret; > +} > +EXPORT_SYMBOL_GPL(iommu_attach_device_shared); > + > +/** > + * iommu_detach_device_shared() - Detach a domain from device > + * @domain: The domain. > + * @dev: The device. > + * > + * The detach helper paired with iommu_attach_device_shared(). > + */ > +void iommu_detach_device_shared(struct iommu_domain *domain, struct device *dev) > +{ > + struct iommu_group *group; > + > + group = iommu_group_get(dev); > + if (!group) > + return; > + > + mutex_lock(&group->mutex); > + if (WARN_ON(!group->attach_cnt || group->domain != domain || > + (group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN && > + group->dma_owner != DMA_OWNER_PRIVATE_DOMAIN_USER))) > + goto unlock_out; > + > + if (--group->attach_cnt == 0) > + __iommu_detach_group(domain, group); > + > +unlock_out: > + mutex_unlock(&group->mutex); > + iommu_group_put(group); > +} > +EXPORT_SYMBOL_GPL(iommu_detach_device_shared);
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