linux-kernel - Re: [RFC 11/19] KVM: x86/mmu: Factor shadow_zero_check out of make

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Date:   Thu, 18 Nov 2021 19:07:08 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     Ben Gardon <bgardon@...gle.com>, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Peter Xu <peterx@...hat.com>,
        Peter Shier <pshier@...gle.com>,
        David Matlack <dmatlack@...gle.com>,
        Mingwei Zhang <mizhang@...gle.com>,
        Yulei Zhang <yulei.kernel@...il.com>,
        Wanpeng Li <kernellwp@...il.com>,
        Xiao Guangrong <xiaoguangrong.eric@...il.com>,
        Kai Huang <kai.huang@...el.com>,
        Keqian Zhu <zhukeqian1@...wei.com>,
        David Hildenbrand <david@...hat.com>
Subject: Re: [RFC 11/19] KVM: x86/mmu: Factor shadow_zero_check out of
 make_spte

On 11/18/21 19:02, Sean Christopherson wrote:
>> 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.
> But shadow is flat out wrong until EPT and NPT support is ripped out of the "legacy"
> MMU.

Yeah, that's true.  "full" MMU? :)

>> - 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
>
> I am all in favor of walk01 and walk12, the guest_mmu vs. nested_mmu confusion
> is painful.
> 
>> - the two MMUs: with nested_mmu gone, root_mmu and guest_mmu are much less
>> confusing and we can keep those names.
>
> I would prefer root_mmu and nested_tdp_mmu.  guest_mmu is misleading because its
> not used for all cases of sp->role.guest_mode=1, i.e. when L1 is not using TDP
> then guest_mode=1 but KVM isn't using guest_mmu.

Ok, that sounds good too.

Paolo