linux-kernel - Re: [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae

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Date:   Thu, 14 Apr 2022 16:12:35 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, kvm@...r.kernel.org,
        Lai Jiangshan <jiangshan.ljs@...group.com>,
        Jonathan Corbet <corbet@....net>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        X86 ML <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        linux-doc@...r.kernel.org
Subject: Re: [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae_root shadow page

On 4/14/22 13:06, Lai Jiangshan wrote:
>> Right, but then load_pdptrs only needs to zap the page before (or
>> instead of) calling kvm_mmu_free_roots().
>>
> 
> Guest PAE page is write-protected instead now (see patch4) and
> kvm_mmu_pte_write() needs to handle this special write operation
> with respect to sp->pae_off (todo).
> And load_pdptrs() doesn't need to check if the pdptrs are changed.

Write-protecting the PDPTR page is unnecessary, the PDPTRs cannot change 
without another CR3.  That should be easy to do in account_shadowed and 
unaccount_shadowed

> I think role.guest_pae_root is needed to distinguish it from
> a sp for a level-3 guest page in a 4-level pagetable.
>
> Or just role.guest_root_level(or role.root_level) and it can replace
> role.passthrough_depth and role.guest_pae_root and role.pae_root.

Yes, I agree.  Though this would also get change patch 1 substantially, 
so I'll wait for you to respin.

Paolo