On Wed, Apr 13, 2022, Paolo Bonzini wrote:
> 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).
It's not redundant, just split out. E.g. if 3 bits are used for the target_level,
a special value is needed to indicate "direct", otherwise KVM couldn't differentiate
between indirect and direct. Violent agreement and all that :-)
I'm ok dropping direct and rolling it into target_level, just so long as we add
helpers, e.g. IIUC they would be
static inline bool is_sp_direct(...)
{
return !sp->role.target_level;
}
static inline bool is_sp_direct_or_passthrough(...)
{
return sp->role.target_level != sp->role.level;
}
> > > 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. :)
LOL, I honestly thought that was a typo. Making it plural sounds like it's passing
through to multiple levels.
