linux-kernel - Re: [PATCH V2 3/7] KVM: X86/MMU: Link PAE root pagetable with its children

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Message-ID: <YoLlzcejEDh8VpoB@google.com>
Date:   Tue, 17 May 2022 00:01:17 +0000
From:   David Matlack <dmatlack@...gle.com>
To:     Lai Jiangshan <jiangshanlai@...il.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Lai Jiangshan <jiangshan.ljs@...group.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: [PATCH V2 3/7] KVM: X86/MMU: Link PAE root pagetable with its
 children

On Tue, May 03, 2022 at 11:07:31PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <jiangshan.ljs@...group.com>
> 
> When special shadow pages are activated, link_shadow_page() might link
> a special shadow pages which is the PAE root for PAE paging with its
> children.
> 
> Add make_pae_pdpte() to handle it.
> 
> The code is not activated since special shadow pages are not activated
> yet.
> 
> Signed-off-by: Lai Jiangshan <jiangshan.ljs@...group.com>
> ---
>  arch/x86/kvm/mmu/mmu.c  | 6 +++++-
>  arch/x86/kvm/mmu/spte.c | 7 +++++++
>  arch/x86/kvm/mmu/spte.h | 1 +
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 126f0cd07f98..3fe70ad3bda2 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -2277,7 +2277,11 @@ static void link_shadow_page(struct kvm_vcpu *vcpu, u64 *sptep,
>  
>  	BUILD_BUG_ON(VMX_EPT_WRITABLE_MASK != PT_WRITABLE_MASK);
>  
> -	spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp));
> +	if (unlikely(sp->role.level == PT32_ROOT_LEVEL &&
> +		     vcpu->arch.mmu->root_role.level == PT32E_ROOT_LEVEL))
> +		spte = make_pae_pdpte(sp->spt);
> +	else
> +		spte = make_nonleaf_spte(sp->spt, sp_ad_disabled(sp));
>  
>  	mmu_spte_set(sptep, spte);
>  
> diff --git a/arch/x86/kvm/mmu/spte.c b/arch/x86/kvm/mmu/spte.c
> index 75c9e87d446a..ccd9267a58ca 100644
> --- a/arch/x86/kvm/mmu/spte.c
> +++ b/arch/x86/kvm/mmu/spte.c
> @@ -251,6 +251,13 @@ u64 make_huge_page_split_spte(u64 huge_spte, int huge_level, int index)
>  	return child_spte;
>  }
>  
> +u64 make_pae_pdpte(u64 *child_pt)
> +{
> +	/* The only ignore bits in PDPTE are 11:9. */
> +	BUILD_BUG_ON(!(GENMASK(11,9) & SPTE_MMU_PRESENT_MASK));
> +	return __pa(child_pt) | PT_PRESENT_MASK | SPTE_MMU_PRESENT_MASK |
> +		shadow_me_value;

If I'm reading mmu_alloc_{direct,shadow}_roots() correctly, PAE page
directories just get: root | PT_PRESENT_MASK | shadow_me_value. Is there
a reason to add SPTE_MMU_PRESENT_MASK or am I misreading the code?

> +}
>  
>  u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled)
>  {
> diff --git a/arch/x86/kvm/mmu/spte.h b/arch/x86/kvm/mmu/spte.h
> index fbbab180395e..09a7e4ba017a 100644
> --- a/arch/x86/kvm/mmu/spte.h
> +++ b/arch/x86/kvm/mmu/spte.h
> @@ -413,6 +413,7 @@ bool make_spte(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp,
>  	       u64 old_spte, bool prefetch, bool can_unsync,
>  	       bool host_writable, u64 *new_spte);
>  u64 make_huge_page_split_spte(u64 huge_spte, int huge_level, int index);
> +u64 make_pae_pdpte(u64 *child_pt);
>  u64 make_nonleaf_spte(u64 *child_pt, bool ad_disabled);
>  u64 make_mmio_spte(struct kvm_vcpu *vcpu, u64 gfn, unsigned int access);
>  u64 mark_spte_for_access_track(u64 spte);
> -- 
> 2.19.1.6.gb485710b
>