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SubjectRe: [RFC v1 00/26] Add TDX Guest Support
On Sun, Apr 4, 2021 at 8:02 AM Dave Hansen <dave.hansen@intel.com> wrote:
>
> It occurred to me that I've been doing a lot of digging in the TDX spec
> lately. I think we can all agree that the "Architecture Specification"
> is not the world's easiest, most disgestable reading. It's hard to
> figure out what the Linux relation to the spec is.
>
> One bit of Documentation we need for TDX is a description of the memory
> states. For instance, it would be nice to spell out the different
> classes of memory, how they are selected, who selects them, and who
> enforces the selection. What faults are generated on each type and who
> can induce those?
>
> For instance:
>
> TD-Private memory is selected by the Shared/Private bit in Present=1
> guest PTEs. When the hardware page walker sees that bit, it walk the
> secure EPT. The secure EPT entries can only be written by the TDX
> module, although they are written at the request of the VMM. The TDX
> module enforces rules like ensuring that the memory mapped by secure EPT
> is not mapped multiple times. The VMM can remove entries. From the
> guest perspective, all private memory accesses are either successful, or
> result in a #VE. Private memory access does not cause VMExits.
>
> Would that be useful to folks?

That paragraph was useful for me as someone coming in cold to TDX
patch review. +1 for more of that style of commentary.

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