Messages in this thread | | | Date | Fri, 20 Jan 2023 13:55:38 -0600 | Subject | Re: [PATCH 1/4] iommu/amd: Introduce Protection-domain flag VFIO | From | "Kalra, Ashish" <> |
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On 1/20/2023 11:50 AM, Jason Gunthorpe wrote: > On Fri, Jan 20, 2023 at 11:01:21AM -0600, Kalra, Ashish wrote: > >> We basically get the RMP #PF from the IOMMU because there is a page size >> mismatch between the RMP table and the IOMMU page table. The RMP table's >> large page entry has been smashed to 4K PTEs to handle page state change to >> shared on 4K mappings, so this change has to be synced up with the IOMMU >> page table, otherwise there is now a page size mismatch between RMP table >> and IOMMU page table which causes the RMP #PF. > > I understand that, you haven't answered my question: > > Why is the IOMMU being programmed with pages it cannot access in the > first place? >
I believe the IOMMU page tables are setup as part of device pass-through to be able to do DMA to all of the guest memory, but i am not an IOMMU expert, so i will let Suravee elaborate on this.
Thanks, Ashish
> Don't do that is the obvious solution there, and preserves huge page > IO performance. > > Jason >
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