linux-kernel - Re: [PATCH v10 032/108] KVM: x86/mmu: Make sync_page not use hard-coded 0 as the initial SPTE value

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Date:   Wed, 9 Nov 2022 11:24:44 +0000
From:   "Huang, Kai" <kai.huang@...el.com>
To:     "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Yamahata, Isaku" <isaku.yamahata@...el.com>
CC:     "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Shahar, Sagi" <sagis@...gle.com>,
        "Aktas, Erdem" <erdemaktas@...gle.com>,
        "isaku.yamahata@...il.com" <isaku.yamahata@...il.com>,
        "dmatlack@...gle.com" <dmatlack@...gle.com>,
        "Christopherson,, Sean" <seanjc@...gle.com>
Subject: Re: [PATCH v10 032/108] KVM: x86/mmu: Make sync_page not use
 hard-coded 0 as the initial SPTE value

On Sat, 2022-10-29 at 23:22 -0700, isaku.yamahata@...el.com wrote:
> From: Isaku Yamahata <isaku.yamahata@...el.com>
> 
> FNAME(sync_page) in arch/x86/kvm/mmu/paging_tmpl.h assumes that the initial
> shadow page table entry (SPTE) is zero.  Remove the assumption by using
> SHADOW_NONPRESENT_VALUE that will be updated from 0 to non-zero value.
> 
> Signed-off-by: Isaku Yamahata <isaku.yamahata@...el.com>
> ---
>  arch/x86/kvm/mmu/paging_tmpl.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
> index 5ab5f94dcb6f..6db3f2b5563a 100644
> --- a/arch/x86/kvm/mmu/paging_tmpl.h
> +++ b/arch/x86/kvm/mmu/paging_tmpl.h
> @@ -1036,7 +1036,8 @@ static int FNAME(sync_page)(struct kvm_vcpu *vcpu, struct kvm_mmu_page *sp)
>  		gpa_t pte_gpa;
>  		gfn_t gfn;
>  
> -		if (!sp->spt[i])
> +		/* spt[i] has initial value of shadow page table allocation */
> +		if (sp->spt[i] == SHADOW_NONPRESENT_VALUE)
>  			continue;
>  
>  		pte_gpa = first_pte_gpa + i * sizeof(pt_element_t);

I think this patch can be merged to previous one?  Looks there's no good reason
to keep it as standalone.