Re: [PATCH 00/16] kvm: arm64: Support for dynamic IPA size

[Will Deacon]

I can comment on one part here:

On Thu, Feb 08, 2018 at 12:18:44PM +0100, Christoffer Dall wrote:
> Wasn't this also the decision taken for IOMMU page table allocation, and
> why was that the right approach for the IOMMU but not for KVM stage 2
> page tables?  Is there room for reuse of the IOMMU page table allocation
> logic in KVM as well?

There were a few reasons we did this for IOMMU page tables:

  * Ability to use different page size/VA bits/levels from the CPU
  * Ability to support different page table formats (e.g. short descriptor)
  * Ability to determine page table attributes at runtime
  * Requirement to map/unmap in atomic context
  * Ability to cope with non-coherent page table walkers
  * Ability to create both stage-1 and stage-2 mappings
  * Easier to hook in our own TLB invalidation routines
  * Support for lockless concurrent map/unmap within confines of the DMA API
    usage

Will