On 18/06/2019 18:05, Jacob Pan wrote: > On Tue, 18 Jun 2019 15:22:20 +0100 > Jean-Philippe Brucker <jean-philippe.brucker@xxxxxxx> wrote: > >> On 11/06/2019 19:13, Jacob Pan wrote: >>>>>> +/** >>>>>> + * ioasid_find - Find IOASID data >>>>>> + * @set: the IOASID set >>>>>> + * @ioasid: the IOASID to find >>>>>> + * @getter: function to call on the found object >>>>>> + * >>>>>> + * The optional getter function allows to take a reference to >>>>>> the found object >>>>>> + * under the rcu lock. The function can also check if the object >>>>>> is still valid: >>>>>> + * if @getter returns false, then the object is invalid and NULL >>>>>> is returned. >>>>>> + * >>>>>> + * If the IOASID has been allocated for this set, return the >>>>>> private pointer >>>>>> + * passed to ioasid_alloc. Private data can be NULL if not set. >>>>>> Return an error >>>>>> + * if the IOASID is not found or does not belong to the set. >>>>> >>>>> Perhaps should make it clear that @set can be null. >>>> >>>> Indeed. But I'm not sure allowing @set to be NULL is such a good >>>> idea, because the data type associated to an ioasid depends on its >>>> set. For example SVA will put an mm_struct in there, and auxiliary >>>> domains use some structure private to the IOMMU domain. >>>> >>> I am not sure we need to count on @set to decipher data type. >>> Whoever does the allocation and owns the IOASID should knows its >>> own data type. My thought was that @set is only used to group IDs, >>> permission check etc. >>> >>>> Jacob, could me make @set mandatory, or do you see a use for a >>>> global search? If @set is NULL, then callers can check if the >>>> return pointer is NULL, but will run into trouble if they try to >>>> dereference it. >>> A global search use case can be for PRQ. IOMMU driver gets a IOASID >>> (first interrupt then retrieve from a queue), it has no idea which >>> @set it belongs to. But the data types are the same for all IOASIDs >>> used by the IOMMU. >> >> They aren't when we use a generic SVA handler. Following a call to >> iommu_sva_bind_device(), iommu-sva.c allocates an IOASID and store an >> mm_struct. If auxiliary domains are also enabled for the device, >> following a call to iommu_aux_attach_device() the IOMMU driver >> allocates an IOASID and stores some private object. >> >> Now for example the IOMMU driver receives a PPR and calls >> ioasid_find() with @set = NULL. ioasid_find() may return either an >> mm_struct or a private object, and the driver cannot know which it is >> so the returned value is unusable. > I think we might have a misunderstanding of what ioasid_set is. Or i > have misused your original intention for it:) So my understanding of an > ioasid_set is to identify a sub set of IOASIDs that > 1. shares the same data type > 2. belongs to the same permission group, owner. In my case it's mostly #1. The two IOASID sets (SVA and AUX) are managed by different modules (iommu-sva and arm-smmu-v3). Since we don't do scalable IOV, the two sets are shared_ioasid and private_ioasid, with either an mm or NULL as private data (but we might need to store a domain for private IOASIDs at some point). So at the moment passing a NULL set to ioasid_find() would work for us as well. However in a non-virtualization scenario, a device driver could define its own set and allocate an IOASID for its own use, associating some private structure with it. If it somehow causes a PRQ on that IOASID, the IOMMU driver shouldn't attempt to access the device driver's private structure. So I do think we need to be careful with global ioasid_find(). Given that any driver in the system can use the allocator, we won't be able to keep assuming that all objects stored in there are of one type. > Our usage is #2., we put a mm_struct as the set to do permission > check. E.g VFIO can check guest PASID ownership based on QEMU process > mm. This will make sure IOASID allocated by one guest can only be used > by the same guest. > > For IOASID used for sva bind, let it be native or guest sva, we always > have the same data type. Therefore, when page request handler gets > called to search with ioasid_find(), it knows its data type. An > additional flag will tell if it is a guest bind or native bind. > > I was under the assumption that aux domain and its IOASID is a 1:1 > mapping, there is no need for a search. Or even it needs to search, it > will be searched by the same caller that did the allocation, therefore > it knows what private data type is. > > In addition, aux domain is used for request w/o PASID. And PPR for > request w/o PASID is not to be supported. So there would not be a need > to search from page request handler. > > Now if we take the above assumption away, and use ioasid_set strictly > to differentiate the data types (Usage #1). Then I agree we can get > rid of NULL set and global search. > > That would require we converge on the generic sva_bind for both > native and guest. The additional implication is that VFIO layer has to > be SVA struct aware in order to sanitize the mm_struct for guest bind. > i.e. check guest ownership by using QEMU process mm. Whereas we have > today, VFIO just use IOASID set as mm to check ownership, no need to > know the type. Thanks for the explanation, I think I understand a little better after taking a closer look at your v4. > Can we keep the NULL set for now and remove it __after__ we converge on > the sva bind flows? Sure, let's revisit this later Thanks, Jean
