Re: [RFC 11/19] KVM: x86/mmu: Factor shadow_zero_check out of make_spte

From: Paolo Bonzini
Date: Thu Nov 18 2021 - 12:19:23 EST

On 11/18/21 17:37, Sean Christopherson wrote:
It's a bit ugly in that we'd pass both @kvm and @vcpu, so that needs some more
thought, but at minimum it means there's no need to recalc the reserved bits.

Ok, I think my final vote is to have the reserved bits passed in, but with the
non-nested TDP reserved bits being computed at MMU init.

Yes, and that's also where I was getting with the idea of moving part of the "direct" MMU (man, naming these things is so hard) to struct kvm: split the per-vCPU state from the constant one and initialize the latter just once. Though perhaps I was putting the cart slightly before the horse.

On the topic of naming, we have a lot of things to name:

- the two MMU codebases: you Googlers are trying to grandfather "legacy" and "TDP" into upstream, but that's not a great name because the former is used also when shadowing EPT/NPT. I'm thinking of standardizing on "shadow" and "TDP" (it's not perfect because of the 32-bit and tdp_mmu=0 cases, but it's a start). Maybe even split parts of mmu.c out into shadow_mmu.c.

- the two walkers (I'm quite convinced of splitting that part out of struct kvm_mmu and getting rid of walk_mmu/nested_mmu): that's easy, it can be walk01 and walk12 with "walk" pointing to one of them

- the two MMUs: with nested_mmu gone, root_mmu and guest_mmu are much less confusing and we can keep those names.