linux-kernel - Re: [RFC PATCH 6/6] KVM: X86: Use level_promoted and pae

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Message-ID: <YdS0J1mmpYmD4KcL@google.com>
Date:   Tue, 4 Jan 2022 20:55:03 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Lai Jiangshan <laijs@...ux.alibaba.com>,
        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@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [RFC PATCH 6/6] KVM: X86: Use level_promoted and pae_root shadow
 page for 32bit guests

On Fri, Dec 10, 2021, Lai Jiangshan wrote:
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.h b/arch/x86/kvm/mmu/tdp_mmu.h
> index 476b133544dd..822ff5d76b91 100644
> --- a/arch/x86/kvm/mmu/tdp_mmu.h
> +++ b/arch/x86/kvm/mmu/tdp_mmu.h
> @@ -100,13 +100,8 @@ static inline bool is_tdp_mmu(struct kvm_mmu *mmu)
>  	if (WARN_ON(!VALID_PAGE(hpa)))
>  		return false;
>  
> -	/*
> -	 * A NULL shadow page is legal when shadowing a non-paging guest with
> -	 * PAE paging, as the MMU will be direct with root_hpa pointing at the
> -	 * pae_root page, not a shadow page.
> -	 */
>  	sp = to_shadow_page(hpa);
> -	return sp && is_tdp_mmu_page(sp) && sp->root_count;
> +	return is_tdp_mmu_page(sp) && sp->root_count;
>  }

is_page_fault_stale() can get similar treatment

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e8c69c2dfbd9..9ff8e228b55e 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3855,19 +3855,7 @@ static bool is_page_fault_stale(struct kvm_vcpu *vcpu,
 {
        struct kvm_mmu_page *sp = to_shadow_page(vcpu->arch.mmu->root_hpa);

-       /* Special roots, e.g. pae_root, are not backed by shadow pages. */
-       if (sp && is_obsolete_sp(vcpu->kvm, sp))
-               return true;
-
-       /*
-        * Roots without an associated shadow page are considered invalid if
-        * there is a pending request to free obsolete roots.  The request is
-        * only a hint that the current root _may_ be obsolete and needs to be
-        * reloaded, e.g. if the guest frees a PGD that KVM is tracking as a
-        * previous root, then __kvm_mmu_prepare_zap_page() signals all vCPUs
-        * to reload even if no vCPU is actively using the root.
-        */
-       if (!sp && kvm_test_request(KVM_REQ_MMU_RELOAD, vcpu))
+       if (is_obsolete_sp(vcpu->kvm, sp))
                return true;

        return fault->slot &&

>  #else
>  static inline bool kvm_mmu_init_tdp_mmu(struct kvm *kvm) { return false; }
> -- 
> 2.19.1.6.gb485710b
>