On 2022/4/13 7:36, Tian, Kevin wrote:
From: Lu Baolu <[email protected]> Sent: Tuesday, April 12, 2022 8:53 PM+ if (!handle) { + ret = -ENOMEM; + goto out_put_ioas; + } + + /* The reference to ioas will be kept until domain free. */ + domain = iommu_sva_alloc_domain(dev, ioas);Shouldn't we first try whether existing domains are compatible to this device?If we think that here domain represents a hardware pagetable actually used by IOMMU for a {device, pasid}, we are able to use per-{device, pasid} domain without checking compatibility. Sharing a domain among devices under the same IOMMU may be an optimization. That could be done in the IOMMU driver just like what vt-d driver is doing for pass-through DMA domains.there is only one hardware page table per mm in this case. Multiple domains are required only due to compatibility reason as Jason/Robin pointed out in SMMU case. Given all other places create multiple domains per ioas only upon incompatibility, probably it's more consistent to doing so in this path too...
Sharing domain for compatible devices is valuable when the domain supports map/unmap operations. That can reduce the number of map/unmap calls and the resulting synchronization of IOTLB. But for SVA case, it's a dumb domain which only provides attach/detach operations. A similar case could be found on pass-through DMA domains. The iommu core allocates a default domain for each group although all the domains represent a same page table for the compatible devices. The VT-d driver optimizes this by exporting a static identity domain. Anyway, I am open for this. I can add a compatible domain list if most of you like that way. :-) Best regards, baolu _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
