linux-kernel - Re: [RFC PATCH v5 033/104] KVM: x86: Add infrastructure for stolen GPA bits

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Date:   Wed, 6 Apr 2022 13:26:01 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Kai Huang <kai.huang@...el.com>, isaku.yamahata@...el.com,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     isaku.yamahata@...il.com, Jim Mattson <jmattson@...gle.com>,
        erdemaktas@...gle.com, Connor Kuehl <ckuehl@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>
Subject: Re: [RFC PATCH v5 033/104] KVM: x86: Add infrastructure for stolen
 GPA bits

On 4/6/22 04:23, Kai Huang wrote:
>>
>>>>
>>>>   
>>>> -		gfn = gpte_to_gfn(gpte);
>>>> +		gfn = gpte_to_gfn(vcpu, gpte);
>>>>   		pte_access = sp->role.access;
>>>>   		pte_access &= FNAME(gpte_access)(gpte);
>>>>   		FNAME(protect_clean_gpte)(vcpu->arch.mmu, &pte_access, gpte);
>>>
>>> In commit message you mentioned "Don't support stolen bits for shadow EPT" (you
>>> actually mean shadow MMU I suppose), yet there's bunch of code change to shadow
>>> MMU.
>>
>> It's a bit ugly, but it's uglier to keep two versions of gpte_to_gfn.
> 
> gpte_to_gfn() is only used in paging_tmpl.h.  Could you elaborate why we need to
> keep two versions of it?

You're right.  Yeah, considering page table walks are not supported when 
private memory is available, it shouldn't be necessary to change 
paging_tmpl.h.

Paolo