Re: [PATCH 00/12] iommufd: Add nesting infrastructure

[Baolu Lu]

On 2023/3/9 16:08, Yi Liu wrote:
> Nested translation is a hardware feature that is supported by many modern
> IOMMU hardwares. It has two stages (stage-1, stage-2) address translation
> to get access to the physical address. stage-1 translation table is owned
> by userspace (e.g. by a guest OS), while stage-2 is owned by kernel. Changes
> to stage-1 translation table should be followed by an IOTLB invalidation.

The last sentence is not always true. If any entry of the stage-1
translation table is changed from non-present to present, the IOTLB has
no chance to cache it yet. Hence there's no need for invalidation.

Best regards,
baolu