On 4/13/22 16:42, Sean Christopherson wrote:
On Wed, Apr 13, 2022, Paolo Bonzini wrote:
On 4/12/22 23:31, Sean Christopherson wrote:
We don't need 4 bits for this. Crossing our fingers that we never had to shadow
a 2-level guest with a 6-level host, we can do:
unsigned passthrough_delta:2;
Basically, your passthrough_delta is level - glevel in Jiangshan's patches.
You'll need 3 bits anyway when we remove direct later (that would be
passthrough_delta == level).
Are we planning on removing direct?
I think so, it's redundant and the code almost always checks
direct||passthrough (which would be passthrough_delta > 0 with your scheme).
Regarding the naming:
* If we keep Jiangshan's logic, I don't like the glevel name very much, any
of mapping_level, target_level or direct_level would be clearer?
I don't love any of these names, especially glevel, because the field doesn't
strictly track the guest/mapping/target/direct level. That could obviously be
remedied by making it valid at all times, but then the role would truly need 3
bits (on top of direct) to track 5-level guest paging.
Yes, it would need 3 bits but direct can be removed.
* If we go with yours, I would call the field "passthrough_levels".
Hmm, it's not a raw level though.
Hence the plural. :)
Paolo
