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From:   Lai Jiangshan <jiangshanlai@gmail.com>
Date:   Thu, 14 Apr 2022 19:06:11 +0800
Message-ID: <CAJhGHyDYeQGUWmco=c4TA1uu=33ccW7z0fDLuYjvkGFW5WnDSQ@mail.gmail.com>
Subject: Re: [RFC PATCH V3 3/4] KVM: X86: Alloc role.pae_root shadow page
To:     Paolo Bonzini <pbonzini@redhat.com>
Cc:     Sean Christopherson <seanjc@google.com>,
        LKML <linux-kernel@vger.kernel.org>, kvm@vger.kernel.org,
        Lai Jiangshan <jiangshan.ljs@antgroup.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        X86 ML <x86@kernel.org>, "H. Peter Anvin" <hpa@zytor.com>,
        linux-doc@vger.kernel.org
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On Thu, Apr 14, 2022 at 6:04 PM Paolo Bonzini <pbonzini@redhat.com> wrote:
>
> On 4/14/22 11:32, Lai Jiangshan wrote:
> > kvm_mmu_free_roots() can not free those new types of sp if they are still
> > valid.  And different vcpu can use the same pae root sp if the guest cr3
> > of the vcpus are the same.
>
> 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.

The semantics will be changed. When the guest updates its PAE root,
the hwTLB will not be updated/flushed immediately until some change
to CRx, but after this change, it will be flushed immediately.

Could we fix 5-level NPT L0 for 4-level NPT L1 only first? it is
a real bug.  I separated it out when I tried to implement one-off
shadow pages.