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

From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <seanjc@google.com>, Ben Gardon <bgardon@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
	Peter Xu <peterx@redhat.com>, Peter Shier <pshier@google.com>,
	David Matlack <dmatlack@google.com>,
	Mingwei Zhang <mizhang@google.com>,
	Yulei Zhang <yulei.kernel@gmail.com>,
	Wanpeng Li <kernellwp@gmail.com>,
	Xiao Guangrong <xiaoguangrong.eric@gmail.com>,
	Kai Huang <kai.huang@intel.com>,
	Keqian Zhu <zhukeqian1@huawei.com>,
	David Hildenbrand <david@redhat.com>
Subject: Re: [RFC 11/19] KVM: x86/mmu: Factor shadow_zero_check out of make_spte
Date: Thu, 18 Nov 2021 18:19:05 +0100	[thread overview]
Message-ID: <db8a2431-8a05-bd50-dd79-74c814c71edd@redhat.com> (raw)
In-Reply-To: <YZaBSf+bPc69WR1R@google.com>

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.

Paolo