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

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Date:   Thu, 14 Apr 2022 19:06:11 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     Paolo Bonzini <pbonzini@...hat.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 Thu, Apr 14, 2022 at 6:04 PM Paolo Bonzini <pbonzini@...hat.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.